[AL, Search]: Expanding test coverage.

Converts SearchLoaderTest to be a parametrized test. Adds data class for
test parametrization. Uses the class to generate searches that vary
query and modified time.

Change-Id: I4be5c9226173ddfe8067d0de5f4df6d2fc2e1d91
Test: increasing test coverage
Flag: com.android.documentsui.flags.use_search_v2
Bug: 378590632