Add image size picker improvements

[cameronvoell]

Fixes #1452

Companion PR's

Gutenberg PR: WordPress/gutenberg#19232
WPiOS PR (for testing): wordpress-mobile/WordPress-iOS#13052

Changes

• Introduces cycle button UI for updating the size of an image from the BottomSheet menu in an Image Block.
• Removes duplicated default image size declarations and instead utilizes image sizes from the editor settings data store.

Screenshots

See this comment and above comments for context: WordPress/gutenberg#17245 (review)

To Test:

1. Navigate to the Block Editor
2. Add an Image Block and upload an image
3. Click the gear for block settings
4. Tap Image Size row and verify value cycles through available sizes (Thumbnail, Medium, Large, Fullscreen).
5. Verify the Image size changes as you click through the menu.
6. Verify the Image Size is preserved if you update the post, leave, and return.

*Note this PR is mainly covering UI updates, for Image Size error handling with updating URL's from the network etc, see this issue: #1593

Update release notes:

• If there are user facing changes, I have added an item to RELEASE-NOTES.txt.

[hypest]

👋 Cameron, is this PR still relevant? If yes, let's retarget it, thanks!

[etoledom]

Thank you @cameronvoell for the update!

@iamthomasbishop - What do you think about this (temporal) solution for the Image Sizes picker?

[iamthomasbishop]

@etoledom @cameronvoell It looks pretty solid overall, based on the test build I grabbed here. One thing I noticed is that the first time you switch to each different size, the background container (with the image block icon and light gray background) is displayed at full size for a split second. Video for reference: https://cloudup.com/c642ckhMCez

[cameronvoell]

One thing I noticed is that the first time you switch to each different size, the background container (with the image block icon and light gray background) is displayed at full size for a split second.

@iamthomasbishop The improvements from this fix should make this much less jarring, especially in dark mode.

[etoledom]

Moved milestone to v1.22.
Please feel free to re-target if you consider this PR must be shipped together with v1.21.

[etoledom]

🎉

[cameronvoell]

closing as gutenberg changes were brought in to gb-mobile through another PR (still under DEV flag).

See this PR for removing DEV flag and updating release notes for this feature: #1904