PM: Restrict subclass construction.

Don't construct a random class just because you were asked to.

Bug: 373467684
Test: atest PackageParsingPerfTest
Flag: EXEMPT bugfix
(cherry picked from commit 65c1a90b)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:b6af52a75354b862781c7b46466c3356791c5599)
Merged-In: I328eca7b8de1eab637e3991adeb2e1d147c30268
Change-Id: I328eca7b8de1eab637e3991adeb2e1d147c30268