[Gutenberg] Preload wp/v2/media using the OPTIONS method to manage `upload_files` capability

[imath]

Hi.

As @aduth explained in this ​PR, it will be needed to update preloaded paths so that they include the wp/v2/media endpoint (using the OPTIONS method). This way of checking the upload_files caps using the Allow header of the result of the endpoint request has been advised by @danielbachhuber.

The Media blocks UI/Featured image section of the document sidebar when the user has the contributor role should be improved.

As this role cannot upload_files the Upload / Drag and drop controls & the Media Library shouldn't be available.

The attached patch makes sure it's possible to preload this specific path using the OPTIONS method without editing the other paths (eg: grouping them into a GET array attribute)

[danielbachhuber]

In 45194.2.diff:

• Apply a block_editor_preload_paths filter to allow plugins / themes to preload additional paths.
• Enforce strict format of $path with is_array( $path ) && 2 === count( $path ).

[danielbachhuber]

In 43833:

Block Editor: Preload wp/v2/media with OPTIONS for caps check.

Also introduces a block_editor_preload_paths filter for plugins and themes to preload additional data.

Props imath, mattheu.
Fixes #45194.

[danielbachhuber]

Reopened for merge to trunk.

[pento]

In 44172:

Block Editor: Preload wp/v2/media with OPTIONS for caps check.

Also introduces a block_editor_preload_paths filter for plugins and themes to preload additional data.

Merges [43833] from the 5.0 branch to trunk.

Props imath, mattheu, danielbachhuber.
Fixes #45194.