In `register_block_type`, continue to allow passing arrays as the `editor_script`, `script`, `view_script`, `editor_style`, and `style` arguments. Note that those fields were soft-deprecated in favor of their `_handles` counterparts in [54155], which would allow specifying multiple items. At the same time, the deprecated fields were limited to `string` or `null`.
However, this broke existing code that passed an array as one of those arguments. For backwards compatibility, this change thus restores the previous behavior. It is implemented in `WP_Block_Type` as a pair of `__get()` and `__set()` methods that wrap around the corresponding `_handles` members, which are arrays of strings.
It also affects the REST API endpoint for block types. The latter’s schema has never allowed for anything other than `string` or `null` for any of those fields. For this reason, it now returns the first element of the array stored in the corresponding `_handles` member in `WP_Block_Type`.
Follow-up [54155].
Props nendeb55, costdev, gziolo, spacedmonkey, mukesh27, sergeybiryukov, audrasjb.
Fixes#56707.
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