* Cherry picks of Binder fixes in Flow

Addresses: https://github.com/vaadin/framework/issues/9000

Addresses:  https://github.com/vaadin/framework/issues/11109

These changes are adopted from https://github.com/vaadin/flow/pull/4138 and https://github.com/vaadin/flow/pull/6757

Fixes #9917

* Add missing null check to Binding

Fixes #10476

Binder.setReadonly will ignore bindings with null setter
or property without an accessible setter when changing
field read only flag.

Fixes #10252

This patch also adds ValueChangeEvent as a parameter to field value change method in Binder.

* Simplify lambda expressions

And remove unneeded 'return' keyword.

* Format

Fixes #9792

Also removes dependency on junit.framework.TestCase .

This allows using BindingBuilder either in a type safe chained manner or with separate calls for the same instance at the cost of less strict type checking.

Fixes #9927
Fixes #9619

Changed values are now only applied to the bean when they pass both field and bean validation. Any change that breaks validation will be pending and is attempted to apply when another change event comes.

This patch also makes the order of status change event handler and listener call order.

This addresses some of the issues raised in #9955.

This patch adds an API to Binding for accessing the validation status handlers from a custom BinderValidationStatusHandler.

Fixes and improves on PR #9932.

Fixes #9427

Calling readBean(null) should reset the form state to the initial state
it was in before calling writeBean(bean)

* Add clear field values #8287

Added functionality to make it possible to clear bound field values manually
or when setting a null bean to binder.

Binder will now clear bound fields for setBean(null) or if using readBean() functionality
when calling the clear() method. Binder.clear() will throw a IllegalStateException if
we have a bound bean.

* MultiSelectionModel MultiSelect should implement emptyValue

* Removing public clear() method and clearing field values only through
setBean(null) and readBean(null) to be consistent and not have
confusing functionality.

* Simplified clearFields() as we don't need to check if field is readOnly

* Document in removeBean JavaDoc that it will also clear the bound fields
if we have a bean the is removed.

* Binder should not have changes after clearing fields.

* Add getEmptyValue as default to MultiSelect.
Multiselect default for empty value should be an empty set.

* Revert "Add getEmptyValue as default to MultiSelect."

This reverts commit 45de8f45c4.

* Merge branch 'master' into issue/8287_Clear_bound_fields

* Remove override for default implementation.

* Fire status change event on clearFields if we had changes before clearing.

* Formatting.

* Add isValid to Binder

isValid enables you to check the current validation
status of a given Binder, without firing events or invoking
handlers.

This patch also clarifies the javadocs of StatusChangeEvents'
hasValidationErrors.

* Throw in Binder.isValid if no bean is set and bean validators exist

* Add test cases to BinderTest

Closes #8232

* Integrate BeanBinder functionality into Binder

BindingBinder is API that is used before calling bind()

Binding is API that is used after calling bind()

The type parameter is mainly used internally, the only externally facing
use is to define the exact type of Binding.getField. Code that has
access to a typed instance of Binding does typically also have direct
access to the field instance, so there's no real use for the type
parameter.

Change-Id: Idf2ab18a79ec5f0a7cef83705b8084fbf7014c10

Unbound binder now correctly sets hasChanges and sends binder
status change events. In addition, hasChanges no longer returns
true in the case where a bean is bound and changes to the bean
were valid.

Change-Id: Ia0a0915c2a205461a2a4b1bfd393413520f863eb

Shorthand for making field show required indicator and validating against empty.
Removes obsolete NotNullValidator and NotEmptyValidator. Latter is still used
in some tests, that why it is still in test packages.

Fixes vaadin/framework8-issues#29

Change-Id: Ib116739a20a0bbd1b1460423ee36ed2752c5496a

save -> writeBean, saveIfValid -> writeBeanIfValid,
load -> readBean, bind -> setBean, unbind -> removeBean.

Now setBean accepts null to reset the bean instead of throwing NPE.

Closes vaadin/framework8-issues#91

Change-Id: I42cbad5856cac11a03bfcefd0fa91a02c41b7234

Fixes vaadin/framework8-issues/#404

Change-Id: I9e07a7de5f67bbd7a5a59cf10cc1a8579cdfbbad

Change-Id: If40bfa28764d1399b5ed4d5928988560e9989dce

This reverts commit 9f672890c1.

Change-Id: I0952a7f9c7efc8a5d7de9987277b835d92d52b39

Change-Id: I1325c629da220317506306fe8f6fff5c0494d9d9

Change-Id: I7c1a55bd68097819e8091533df7232271af689c3

Otherwise any validation triggered by field value changes listeners
would cause errors to be visible after loading a new bean.

Change-Id: I741529f491ae6b36ff2a9aa4326c394cc12fb320

Mostly based on comments on a previous patch that was merged.

Change-Id: I146995853b3318d89061f1d06ab4bbd859168661

Adds an unresolved validation status to make it possible to clear
visible field validation errors, even if status is not yet valid.

Change-Id: I227a8802b6a71be1533dc903bad1a8e2faef5ed2

BinderStatusHandler is now triggered only once per validation.
Unified ValidationError and BinderResult into BinderValidationStatus.
Renamed ValidationStatusChangeEvent into ValidationStatus.
Unified handler names for validation status.

Next patch will fix resetting of field errors on reset.

Change-Id: I9536d554d781fe599fbd7e5bcb5a9ffebe675ca0

Change-Id: Id308bd9b08973804e61706192c96118fd6446d3f

This feature doesn't make a whole lot of sense until
form level status changes are available.

Change-Id: Ie634c4a6b3511b7cbf9e367192034934b0e0d4b0

An item level validator is run on the item (bean) after field validators
have passed. A failed item level validator will block save operations,
just like field level validators.

Change-Id: I3b918b33371ceef07cdfbd0a8b6d477d4ac26b85

Change-Id: I44498b4b34b2e9732b50abb14e8eb7be01314158

Change-Id: I5edf6136f155a9ee5dc5fd6286004f4e8cd8c3db

BinderTest had duplicate tests which are now removed.

Remaining Binding tests are renamed.

Change-Id: I1b572dcdf40a8d6b4e7e0ce8caa943f8aaaf8320