Fix: deleting the last block triggers a focus loss. (#14189)

## Description
This PR fixes a problem: if the post contains one block and it is removed the focus is lost.

This is a regression that happened when removeBlocks action was refactored to be a generator. We had an effect that inserts the default block during remove blocks action when certain conditions are met, this effect stopped working.
This PR removes the effect and makes sure everything is handled by the removeBlocks action creator.

End to end test available at #14191.

## How has this been tested?
I created a new post.
I wrote something in a paragraph I removed the paragraph using the remove button in the side menu and I verified the default block was added.

packages/block-editor/src/store/actions.js

@@ -393,6 +393,17 @@ export function* removeBlocks( clientIds, selectPrevious = true ) {
 		type: 'REMOVE_BLOCKS',
 		clientIds,
 	};
+
+	const count = yield select(
+		'core/block-editor',
+		'getBlockCount',
+	);
+
+	// To avoid a focus loss when removing the last block, assure there is
+	// always a default block if the last of the blocks have been removed.
+	if ( count === 0 ) {
+		yield insertDefaultBlock();
+	}
 }
 
 /**

packages/block-editor/src/store/effects.js

@@ -127,9 +127,6 @@ export default {
 	RESET_BLOCKS: [
 		validateBlocksToTemplate,
 	],
-	REMOVE_BLOCKS: [
-		ensureDefaultBlock,
-	],
 	REPLACE_BLOCKS: [
 		ensureDefaultBlock,
 	],

packages/block-editor/src/store/test/actions.js

@@ -28,6 +28,7 @@ import {
 	toggleBlockMode,
 	updateBlockListSettings,
 } from '../actions';
+import { select } from '../controls';
 
 describe( 'actions', () => {
 	describe( 'resetBlocks', () => {
@@ -218,6 +219,10 @@ describe( 'actions', () => {
 					type: 'REMOVE_BLOCKS',
 					clientIds,
 				},
+				select(
+					'core/block-editor',
+					'getBlockCount',
+				),
 			] );
 		} );
 	} );
@@ -234,10 +239,14 @@ describe( 'actions', () => {
 					type: 'REMOVE_BLOCKS',
 					clientIds: [ clientId ],
 				},
+				select(
+					'core/block-editor',
+					'getBlockCount',
+				),
 			] );
 		} );
 
-		it( 'should return REMOVE_BLOCKS action, opting out of remove previous', () => {
+		it( 'should return REMOVE_BLOCKS action, opting out of select previous', () => {
 			const clientId = 'myclientid';
 
 			const actions = Array.from( removeBlock( clientId, false ) );
@@ -247,6 +256,10 @@ describe( 'actions', () => {
 					type: 'REMOVE_BLOCKS',
 					clientIds: [ clientId ],
 				},
+				select(
+					'core/block-editor',
+					'getBlockCount',
+				),
 			] );
 		} );
 	} );