Add end 2 end test to block switcher with removed blocks

[jorgefilipecosta]

Description

This PR's adds tests that make sure the block switcher works correctly even when some blocks are removed.
This test changes should catch the bug fixed in #12192.

How has this been tested?

Verify the end 2 end tests pass.
Apply the following patch the reverts
#12192 and verify the end 2 end tests fail:

diff --git a/packages/editor/src/components/block-switcher/index.js b/packages/editor/src/components/block-switcher/index.js
index adc4bf4ef..390e6a7f3 100644
--- a/packages/editor/src/components/block-switcher/index.js
+++ b/packages/editor/src/components/block-switcher/index.js
@@ -47,7 +47,7 @@ export class BlockSwitcher extends Component {
 		const possibleBlockTransformations = orderBy(
 			filter(
 				getPossibleBlockTransformations( blocks ),
-				( block ) => block && !! itemsByName[ block.name ]
+				( block ) => !! itemsByName[ block.name ]
 			),
 			( block ) => itemsByName[ block.name ].frecency,
 			'desc'

[tofumatt]

Looks good to me! 👍

[jorgefilipecosta]

Thank you for your review and your tweaks @tofumatt!