Pattern overrides: Update overrides attribute data structure and rename it to content

[talldanwp]

In the Gutenberg PR ​#58596, some changes were made to the data structure of the pattern overrides stored in the pattern block and consequently passed to the core/pattern-overrides block binding handler. Read there for more information on the reasoning.

Some of these changes need to be backported to WordPress core, so I'm creating this ticket for that change.

Backports the changes from ​https://github.com/WordPress/gutenberg/pull/58596.

The gutenberg PR changes the data structure of the overrides data to allow it to be more flexible for future features.

Trac ticket: [](https://core.trac.wordpress.org/ticket/60456)

@talldan, when you are done with all the backports, it would be great to add some basic PHPUnit tests covering how Pattern Overrides work with block bindings. It could be on the _block_bindings_pattern_overrides_get_value level to start with. However, more useful would be to have some integration test that runs do_blocks( '' ) (I had the old format in my local instance).

[youknowriad]

In 57585:

Editor: Update pattern overrides attribute format.

Updates the pattern block's overrides attribute data structure and renames it to content.
This new format should prove more flexible for the future.

Props talldanwp, gziolo.
Fixes #60456.

commit https://core.trac.wordpress.org/changeset/57585

[hellofromTonya]

#60454 was marked as a duplicate.