refactor(selection): keep setSelectedBlocks logic simple

[fundon]

1. click a image, selection.state.type switch to embed
2. drag-and-drop image block, selection.state.type switch to block

The following methods are all for block:

blocksuite/packages/blocks/src/page-block/default/selection-manager/utils.ts

Lines 144 to 148 in 9df30f4

	state.selectedBlocks = selectedBlocks;
	state.type = selectionType ?? state.type;
	if (rects) {
	slots.selectedRectsUpdated.emit(rects);

I think we can set the state after the drag and drop to block first to avoid confusion.

[codesandbox]

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[doodlewind]

Thanks for the fix!