Add tooltips for MD editor buttons and add `muted` class for buttons (#23896)

Followup of #23876 according to my unreleased review demanding tooltips.
Additionally
- add a `muted` equivalent for buttons
- convert `switch to legacy` to an actual button
- enroll `switch to legacy` in the builtin pseudo focus cycle
- remove spaces between the buttons

The effect of the `muted` class is what you would expect: The button
loses all of its normal styling, and is defined only by its content instead.
This will help reduce a11y infractions in the future, as that was one of
the major points why people didn't use `<button>` tags and decided on a
bad fix (i.e. through `<div>`s) instead.

## Appearance

![image](https://user-images.githubusercontent.com/51889757/229510842-337378e5-faa5-4886-a910-08614c0c233d.png)

---------

Co-authored-by: silverwind <me@silverwind.io>

2 files changed, 16 insertions, 3 deletions

diff --git a/web_src/css/base.css b/web_src/css/base.css
index c48a36c854..7640f15244 100644
--- a/web_src/css/base.css
+++ b/web_src/css/base.css
@@ -328,14 +328,27 @@ progress::-moz-progress-bar {
   user-select: none;
 }
 
+.btn-link {
+  background: none;
+  border: none;
+  color: var(--color-primary);
+}
+
+a:hover,
+.btn-link:hover {
+  text-decoration: underline;
+}
+
 a,
-.ui.breadcrumb a {
+.ui.breadcrumb a,
+.btn-link {
   color: var(--color-primary);
   cursor: pointer;
   text-decoration-skip-ink: all;
 }
 
 a.muted,
+.btn-link.muted,
 .muted-links a {
   color: inherit;
 }
@@ -343,6 +356,7 @@ a.muted,
 a:hover,
 a.muted:hover,
 a.muted:hover [class*="color-text"],
+.btn-link.muted:hover,
 .muted-links a:hover,
 .ui.breadcrumb a:hover {
   color: var(--color-primary);
diff --git a/web_src/css/editor-markdown.css b/web_src/css/editor-markdown.css
index 1a09b5d596..df3f756c57 100644
--- a/web_src/css/editor-markdown.css
+++ b/web_src/css/editor-markdown.css
@@ -9,13 +9,12 @@
 }
 
 .combo-markdown-editor .markdown-toolbar-group {
-  display: inline-block;
+  display: flex;
 }
 
 .combo-markdown-editor .markdown-toolbar-button {
   user-select: none;
   padding: 5px;
-  cursor: pointer;
 }
 
 .ui.form .combo-markdown-editor textarea.markdown-text-editor,