Block Templates: Add the custom templates info for the template posts

[Mamaduka]

What?

Fixes #43557.

PR updates _build_block_template_result_from_post to include postTypes details defined in theme.json for modified custom templates. Also, add logic to the get_block_templates for skipping these templates when post type argument is provided.

Testing Instructions

Using TT2 theme.

1. Go to the Site Editor.
2. Modify the "Page (No Separators)" template.
3. Open a post.
4. Confirm "Page (No Separators)" isn't available in Template dropdown.

Screenshots or screencast

[Aljullu]

It works for me and fixes the issue. Thanks for working on it, @Mamaduka!

I'm not sure about the process to merge these things into WP core, should I close my PR because this is going to be merged with the WP 6.1 release or should I update it?

[Mamaduka]

Thanks for testing and reviewing, @Aljullu!

I'm not sure about the process to merge these things into WP core, should I close WordPress/wordpress-develop#3131 because this is going to be merged with the WP 6.1 release or should I update it?

The backporting PHP changes is a manual process, so I would recommend updating your PR 👍

Then leave a comment in #43440, so the Editor release leads are aware of the core patch.

[Aljullu]

Thanks for guiding me through the process.

✔️ PR updated: WordPress/wordpress-develop#3131.
✔️ Comment left for the Editor release lead: #43440 (comment).