List Item: Add anchor support

[chiilog]

What?

Added anchor support for list items.

Why?

Sometimes it is necessary to specify an anchor for a list item.

Fixes #29838

How?

Add anchor:true to supports in block.json

Testing Instructions

1. Open a post or page.
2. Insert a list-item block.
3. Open Settings panel.
4. Enter an anchor in HTML ANCHOR in Advanced

Screenshots or screencast

[github-actions]

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[talldan]

Thanks for making the PR, I decided to go with merging #48758 instead as it was the first PR created to solve the problem (and it's identical to the code in this PR)