Add end 2 end test dynamic allowed blocks

[jorgefilipecosta]

Description

This PR adds a simple end 2 end test that makes sure allowed blocks inside a parent block can be changed dynamically depending on some condition e.g: the number of child's the parent contains.

How has this been tested?

We just need to make sure the test cases pass.

Related: #14515

[gziolo]

I proposed a different name for the lists of allowed blocks. It took me some time to understand why there are two arrays with 2 blocks where one of the constants says less than two :)

[aduth]

I see this test fail intermittently. Do you have any idea why that might be?

I wonder if there might be some issue of race condition where the dynamic changes to the allowed blocks does not update synchronously. I sense this could happen based on how a lot of InnerBlocks implementation relies on synchronizing after some update.

Otherwise, do you have any thoughts on how we could improve the stability of this test? Ideally it's something where we should be able to rely on these changes taking effect immediately, but at worst we could try to update the test to "wait for" some indication that it's been applied.

   ✕ correctly applies dynamic allowed blocks restrictions (3238ms)
  ● Allowed Blocks Setting on InnerBlocks  › correctly applies dynamic allowed blocks restrictions
    expect(received).toEqual(expected)
    Difference:
    - Expected
    + Received
      Array [
    -   "Gallery",
    -   "Video",
    +   "Image",
    +   "List",
      ]
      81 | 		expect(
      82 | 			await getAllBlockInserterItemTitles()
    > 83 | 		).toEqual( [
         | 		  ^
      84 | 			'Gallery',
      85 | 			'Video',
      86 | 		] );
      at Object.toEqual (specs/editor/plugins/inner-blocks-allowed-blocks.test.js:83:5)
          at runMicrotasks (<anonymous>)