feat(cdk-experimental/testing): allow restriction of parent element when using locatorFor(harness)

[mmalerba]

No description provided.

[mmalerba]

CARETAKER NOTE: CatalystHarnessEnvironment tests will need to be updated

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[googlebot]

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[mmalerba]

As discussed with @jelbourn offline, refactored the API to be an option on HarnessPredicate rather than an additional parameter to locatorFor.

Currently blocked on #16848

[mmalerba]

unblocked now that #16848 is in, PTAL

[jelbourn]

LGTM

[ngbot]

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