Fix getting style via $getSelectionStyleValueForProperty when selection is collapsed

[Piliuta]

Fixes #4491

Note: This PR focuses on a fix inside $getSelectionStyleValueForProperty and not on the RangeSelection style property (which I believe should be a long-term fix).

Context:

style property on the RangeSelection was implemented in #3863

however, it was not implemented for the case when selection is not collapsed

lexical/packages/lexical/src/LexicalEvents.ts

Lines 306 to 350 in c09ab73

	if (selection.isCollapsed()) {
	// Badly interpreted range selection when collapsed - #1482
	if (
	domSelection.type === 'Range' &&
	domSelection.anchorNode === domSelection.focusNode
	) {
	selection.dirty = true;
	}
	// If we have marked a collapsed selection format, and we're
	// within the given time range – then attempt to use that format
	// instead of getting the format from the anchor node.
	const windowEvent = getWindow(editor).event;
	const currentTimeStamp = windowEvent
	? windowEvent.timeStamp
	: performance.now();
	const [lastFormat, lastStyle, lastOffset, lastKey, timeStamp] =
	collapsedSelectionFormat;
	if (
	currentTimeStamp < timeStamp + 200 &&
	anchor.offset === lastOffset &&
	anchor.key === lastKey
	) {
	selection.format = lastFormat;
	selection.style = lastStyle;
	} else {
	if (anchor.type === 'text') {
	selection.format = anchorNode.getFormat();
	selection.style = anchorNode.getStyle();
	} else if (anchor.type === 'element') {
	selection.format = 0;
	selection.style = '';
	}
	}
	} else {
	let combinedFormat = IS_ALL_FORMATTING;
	let hasTextNodes = false;
	const nodes = selection.getNodes();
	const nodesLength = nodes.length;
	for (let i = 0; i < nodesLength; i++) {
	const node = nodes[i];
	if ($isTextNode(node)) {
	// TODO: what about style?

Since $getSelectionStyleValueForProperty relies on this property, it does not return the correct value in cases when the selection is not collapsed.

Problem

This method is often used for reflecting current values on toolbars, but it does not work in half (range selection) cases.

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[acywatson]

Thanks for the fix! Sorry I missed all the comments on that issue.