Utils: Preserve omitted ability input

[jorgefilipecosta]

What?

• Preserves omitted runAbility() input as undefined instead of normalizing it to null.
• Omits REST fallback input payloads when the caller does not provide input.
• Keeps explicitly provided empty-object input as request input.

Why?

Some abilities use an object schema with a default empty object for empty collection/query mode. Passing null prevents the abilities client from applying that schema default and can make runAbility( 'core/users' ) fail where executeAbility( 'core/users' ) succeeds.

Core users is at #774.

Testing

• npx wp-scripts test-unit-js tests/unit/run-ability.test.ts
• npm run lint:js -- src/utils/run-ability.ts tests/unit/run-ability.test.ts
• All other tests and checks are green.

[github-actions]

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[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.71%. Comparing base (dd7d364) to head (afb164a).

Additional details and impacted files

@@            Coverage Diff             @@
##             develop     #775   +/-   ##
==========================================
  Coverage      76.71%   76.71%           
  Complexity      1828     1828           
==========================================
  Files             87       87           
  Lines           7764     7764           
==========================================
  Hits            5956     5956           
  Misses          1808     1808           

Flag	Coverage Δ
unit	76.71% <ø> (ø)

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[dkotter]

We don't currently have any unit tests for our TS files. While I'm not opposed to getting that added, that will require more than just a single test file, we'll need all the underlying code to run those tests as well (and get those set up in CI). May be worth doing that in a separate PR instead of rolling into this one

[gziolo]

Approved. Verified locally: install, build, tests, lint, and typecheck all pass. Nice, focused fix.

One small follow-up (not blocking): the GET/DELETE path has no test yet, and an explicit null is treated differently there (no input) than in POST (input: null). Worth a quick test and a decision on that case later.

[dkotter]

Would be great if we can ensure the PR template is followed here. Noticing the Use of AI Tools and Changelog Entry sections aren't provided right now and the Testing Instructions section just includes automated test steps whereas we want manual test steps there