Update FSE plugin to version 1.12.0

[p-jackson]

Changes proposed in this Pull Request

• Version bump
• Changelog

I didn't mention the changes to plans grid or domain picker (which are under development) in the changelog.

Testing instructions

• Apply D45968-code to your sandbox
• Check the donation block content is editable (Donation block: Make content editable #43834)
• Check the launch button records a track event (Gutenboarding: Track when launch button is clicked. #43885)
• Add the nav-sidebar-enabled sticker to your test site (or define WPCOM_BLOCK_EDITOR_SIDEBAR) and check that clicking the (W) opens the nav sidebar

If approving this could you please also approve D45968-code :)

[matticbot]

Test live: https://calypso.live/?branch=update/fse-v1.12

[matticbot]

Caution: This PR affects files in the FSE Plugin on WordPress.com
Please ensure your changes work on WordPress.com before merging.

D45968-code has been created so you can easily test it on your sandbox. See this FieldGuide page about developing in the FSE Plugin for more info: PCYsg-ly5-p2

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[andrewserong]

LGTM! All working nicely for me (except for Donations block, haven't been able to test that one, but it's an in-development feature) 👍