RichText: ignore selection changes during composition

[ellatrix]

Description

This PR fixes input composition after #16875. We're checking selection during keyup now as well, but we shouldn't do that during input composition as the browser will otherwise fail to compose.

This is done already for the selectionchange event:

gutenberg/packages/rich-text/src/component/index.js

Lines 327 to 331 in 005e030

	if ( event && event.nativeEvent.isComposing ) {
	// Also don't update any selection.
	document.removeEventListener( 'selectionchange', this.onSelectionChange );
	return;
	}

Unfortunately I'm not able to write any e2e tests. Puppeteer won't compose characters when given the right sequence of keys, and I'm not succeeding at emulating it. I cannot recreate the internal state and UI that the browser has, and it's this state that gets destroyed if we record any input or selection during composition.

The line under this backtick means that the browser is composing. Any ideas are welcome here.

How has this been tested?

This depends a bit on your keyboard layout. For a US/QWERTY layout:

• Press Alt+`.
• Press a.

The result should be à.

(Puppeteer ignores Alt+` here.)

Screenshots

Types of changes

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.

[youknowriad]

LGTM

[ellatrix]

Thanks for testing!