Enforce the cross-profile intent check.

DocumentsUI currently hard-codes the IntentForwarderActivity class name.
It uses this to determine whether to show a 'switch to personal profile'
button. Essentially, it wants to know if the intent it received is a
cross-profile intent, so it asks package manager which intents can
resolve it and checks whether one of them is IntentForwarderActivity.

This is not CTS-enforced, so this CL ensures that it is. OEMs can remove
or rename IntentForwarderActivity as long as they update this API and
keep the corresponding CTS test passing.

Bug: 149568382
Bug: 136249261
Test: atest CtsDevicePolicyManagerTestCases:com.android.cts.devicepolicy.ManagedProfileCrossProfileTest#testCrossProfileIntentFilters
Change-Id: I51916c13320420068987925ac979e59bef3b660d