Rich Text: Deprecate event proxying

[aduth]

This pull request seeks to deprecate the RichText component's proxyPropEvents function, which handles and propagates a full set of events bound to TinyMCE.

There are a few motivations for this change:

• Performance. We are handling costly events such as mousemove for RichText.
• Explicitness. Be very clear about what props are supported for RichText.
• Consistency. Some callbacks like onChange have transforms applied in addition to the default event handling, and don't pass event as a callback argument.

This was originally introduced in the very first implementation of the autocompleter (#2630), where the autocompleter had applied props directly to the instance of RichText. This was refactored away in #2896.

Many alternatives exist, and are included in the deprecation message:

• Documented props
• Ancestor element event handler
• onSetup and binding events directly to the internal editor instance

Note: This is not expected to have an impact on the majority usage of RichText. The onChange callback still behaves as it did previously.

Testing instructions:

Verify there are no regressions in the behavior of RichText.

Try adding an event like onContextMenu to a RichText element and verify that a deprecation warning occurs.

[aduth]

To clarify, this will start causing warnings on blocks which used the pattern for setting focus on a block via setFocus (i.e. onFocus={ setFocus }), made redundant in #5029 and then explicitly removed in #6352.

Such blocks should just remove onFocus props altogether, as they do not need to handle isSelected themselves. See also #5029.

[youknowriad]

I wonder if we should introduce an explicit onFocus prop, it seems to be something commonly used across blocks even after #5039

[youknowriad]

So it looks like our remaining usage of onFocus is to ensure Image and Gallery captions show the toolbar of the captions when needed. I wonder if we can't automatically handle this similar to #5039 cc @gziolo

[gziolo]

Yes, we can, needs more work on our side. I can schedule it for the next week.

[gziolo]

@youknowriad, I opened #6871 to address the issue you raised.