Slash Inserter: Restrict block list to allowed blocks only

[ssang]

What?

Fixes #64411

This PR forces the WPCompleter block list to show insertable blocks only and fixes a regression introduced by #62169.

Why?

See #64411

#62169 enabled all blocks to be visible in the block list. The WPCompleter component should be restricted to relevant blocks like the QuickInserter

How?

afa0d6e added a isQuick parameter to the useBlockTypesState() call to restrict the quick inserter to a list of relevant blocks. Setting this to true when used in the WPCompleter component forces it to act like a QuickInsterter and only shows relevant blocks.

Testing Instructions

1. Create a block that allows for a subset of blocks including the core/paragraph block as child blocks
2. Insert the paragraph block
3. Type / to start searching for other blocks

Screenshots or screencast

Before Gutenberg version 18.5.0

Gutenberg version ^18.5.0

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[talldan]

The fix is working for me, and it seems like the intended use of the isQuick param.

Thanks again for spotting and fixing the bug.

[talldan]

I've confirmed that the bug is also in WordPress 6.6.1, so I've cherry picked this onto the wp/6.6 branch for release in 6.6.2 - ac02098

[ssang]

Thanks for the quick turnaround. Glad to see it fast forwarded to 6.6.2.

I linked my account to WP if that affects anything. But that doesn't really matter :D