Add skip functionality to package parsing

There are specific cases where a package should be ignored by
whoever is parsing it, either because the device was configured to
ignore it, or the device doesn't support it.

While mostly used for testing, this adds a skip method to
ParseInput and a matching install error code to explicitly express
this case during parsing.

Bug: 155420149

Test: atest com.android.server.pm.parsing

Change-Id: I7eff53544341e21108d9d027f3afe75a1e845f40