Allow legacy components to paint infinity double values again (#19447)

Allow legacy components to paint infinity double values again (#19447)

JsonPaintTarget.addAttribute(String,double) converts infinity values to
{ "name": Infinity }. This is not valid JSON but has "always worked" and
at least NumberField relies on being able to send infinity values.

For state and RPC it's not possible to send 'infinity' as JsonNumber
converts those to null.

It is not possible to send 'infinity' back to the server using a legacy
variable either as also in this case JsonNumber is used and the value becomes
null.

This fix should be reverted when legacy variable support is removed.

Change-Id: I4b5366420e11915236eff447e3eeedc458cf8cea