Move the Pattern Overrides feature to the block editor package

[talldan]

Description

The pattern overrides feature currently exists primarily in the @wordpress/editor package as an extension to the default block editor.

This has caused some issues though, most recently documented in #65058. The added complexity isn't ideal, and it also likely causes some performance issues.

In a brief conversation with recently, @youknowriad mentioned an alternative, that pattern overrides could be considered a @wordpress/block-editor package feature.

Doing so would allow for removing the use of filters/slots to extend parts of the editor, and tidy up the code considerably.

The steps would be:

• Move the pattern overrides registration to the blocked editor package (https://github.com/WordPress/gutenberg/blob/trunk/packages/editor/src/bindings/pattern-overrides.js)
• Examine pattern overrides features that use filters and move them into the block editor package (e.g. https://github.com/WordPress/gutenberg/blob/trunk/packages/editor/src/hooks/pattern-overrides.js)