Don't steal focus when opening browse all blocks

[jeryj]

Fixes #61361

What?

When using the browse all blocks button from adding a new navigation link block, the inserter would steal focus from the popover (correctly) and then the popover would close, stealing focus back.

Why?

Fix using the inserter from the navigabion block.

How?

To prevent this bug, we check to see if focus is still within the popover at the time of closing. If focus is no longer within it, we don't move focus back to the selected block and instead let whatever stole focus keep the focus.

Testing Instructions

• Use the navigation link inserter (+ button)
• Select Add Block
• Select Browse All
• Focus should be in the inserter and the link inserter popover should be closed

Testing Instructions for Keyboard

• Use the navigation link inserter (+ button)
• Select Add Block
• Select Browse All
• Focus should be in the inserter and the link inserter popover should be closed

Escape from Adding block

• Use the navigation link inserter (+ button)
• Select Add Block
• Select Browse All
• Press Escape
• Focus should be on the previous navigation block

Screenshots or screencast

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: jeryj <jeryj@git.wordpress.org>
Co-authored-by: t-hamano <wildworks@git.wordpress.org>
Co-authored-by: talksina <talksina@git.wordpress.org>
Co-authored-by: hagege <hage@git.wordpress.org>
Co-authored-by: annezazu <annezazu@git.wordpress.org>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[t-hamano]

From what I've tested, it works as expected.

Adding E2E tests might help, but since I believe this issue is critical, let's ship this PR to WP6.6.