WordPress 5.7 Compatibility: Primary issue

[jeherve]

WordPress 5.7 is set to release on March 9, 2021:
https://make.wordpress.org/core/5-7/

We consequently need to ensure that Jetpack is fully compatible with this new release.

• Update our "tested up to" version General: update WordPress version requirements to WP 5.6 #18860
• Update the version of WordPress required for Jetpack from WP 5.5 to WP 5.6 General: update WordPress version requirements to WP 5.6 #18860
• Remove WP 5.5 backwards compatibility checks General: update WordPress version requirements to WP 5.6 #18860

In addition to the above, we can follow the dev-notes that will drop here about the release:
https://make.wordpress.org/core/tag/dev-notes+5-7/

• Ensure SSO and Protect are compatible with the latest round of changes to the log in screen (reference)
• Deprecations: Changes to Toolbar components (Reference) General: update WordPress version requirements to WP 5.6 #18860
• Robots API: update Jetpack to use new API when necessary Protect: introduce new wp_robots_no_robots when available #18897 (reference)
• Miscellaneous changes (reference)
• Color changes (reference and ticket) General: update colors to match upcoming WP 5.7 color changes #18916
• Ensure that Inner Blocks API changes do not break the Form block (reference)
• Contact Form: Narrow Editing Window on WordPress 5.7 Form: ensure that the form settings look good in WP 5.7+ #18932

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Extras

• Blocks: switch away from __experimentalBlock to useBlockProps Blocks: switch away from __experimentalBlock to useBlockProps #18864