Implement isPolicyApplied() in PackageSetUnion

Checks if all the packages (stored as strings) from the policy 'value'
are found within the 'resolvedPolicy'

Bug: 285532044

Test: atest com.android.server.devicePolicy.ResolutionMechanismTest#isPolicyApplied_packageSetUnion_setIncluded_returnsTrue
Test: atest com.android.server.devicePolicy.ResolutionMechanismTest#isPolicyApplied_packageSetUnion_setDoesNotIntersect_returnsFalse
Test: atest com.android.server.devicePolicy.ResolutionMechanismTest#isPolicyApplied_packageSetUnion_setPartiallyIncluded_returnsFalse

Flag: TEST_ONLY

Change-Id: I64108c0f7672bb452343b0f27cb47d017008488d