REST API: Small optimizations to filtering by context

[dlh]

As previously ​discussed in Slack, the attached patch proposes some minor optimizations to rest_filter_response_by_context() and adds a few tests.

In the patch:

• Avoid recalculating the schema type with each iteration of the loop.

• If the schema type is an array including both array and object, attempt to use the best type for the given response data (currently, the data is always be treated as array). Includes a test for this case.

• If the type is array and the context of items doesn't match, return an empty array and break out of the loop since each item will be checked against the same schema anyway. Includes a test for this case.

[TimothyBlynJacobs]

Thanks for this @dlh! This looks right to me. Can you make this a PR so we can get the full test suite to run?

The attached patch proposes some minor optimizations to rest_filter_response_by_context() and adds a few tests..

Trac ticket: https://core.trac.wordpress.org/ticket/50700

[TimothyBlynJacobs]

In 48555:

REST API: Optimize rest_filter_response_by_context performance.

In [47758] a new function rest_filter_response_by_context was introduced to expand the JSON schema features supported by the context filtering mechanism.

This commit improves the performance of that function by eliminating repetitive comparisons and loops. Additionally, it improves multi-type support for object + array types.

Fixes #50700.
Props dlh.

Merged into WP Core in https://core.trac.wordpress.org/changeset/48555