Update mobile block editor settings to use Gallery block v2 for WordPress 5.9+

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What?

Attempts to fix an issue where users on WordPress 5.9+ receive the wrong version of the Gallery block.

Related issues:

• Gallery block: Determine galleryWithImageBlocks prop value based on the WordPress version of the site when value is unknown #47782
• Galleries with captioned images no longer function properly wordpress-mobile/WordPress-Android#17712

Why?

When a self-hosted site is using WordPress 5.9+ and the Gutenberg plugin is not installed, the Gallery block defaults to v1. This is due to the prop galleryWithImageBlocks being unknown.

How?

In the mobile block editor settings, the list and quote blocks are instructed to use v2 versions. This PR introduces a similar instruction for the Gallery block for sites using WP 5.9+. (This technique was also used when the Gallery block v1 was temporarily deprecated, which has since been reverted.)
Caveat: I noted that as this code is in lib/experiments, it may not be available to users without the Gutenberg plugin installed, which is the group that would benefit the most from this change. However, perhaps this PR could be a starting point for how we leverage a similar technique to provide either the WP version number or the galleryWithImageBlocks flag itself to users without the plugin installed.

Testing Instructions

1. Create a self-hosted site with WordPress version 5.9 or above.
2. Check that the Gutenberg plugin is not installed. If not, uninstall it.
3. Create a post.
4. Insert a Gallery block.
5. Observe that the Gallery block is v2 (content is rendered using inner blocks).
6. Repeat the above steps for a self-hosted site using WordPress 5.8 or below.
7. Observe that the Gallery block is using v1 (content is rendered using inner blocks).

[derekblank]

Closing in favor of handling this in the main apps.