Add missing unit tests for plan cache functionality.

For current file coverage see the spreadsheet.

Coverage under 80%:

src/mongo/db/query/plan_cache/classic_plan_cache.cpp (45%)

src/mongo/db/query/plan_cache/plan_cache_invalidator.cpp (65%)

src/mongo/db/query/plan_cache/sbe_plan_cache.cpp (72%)

src/mongo/db/query/plan_cache/sbe_plan_cache_on_parameter_change.cpp (50%)