Clean up GetSystemProperty.* APIs

1. Factor out duplicated implementation of
   GetSystemPropertyUint32 on host/linux/android
2. Add GetSystemPropertyBool and factor out the code
   for retrieving bool properties in system/gd/hal/snoop_logger.cc

Bug: 263323082
Test: refactoring CL. Existing unit tests still pass.

Dirty-cherry because of missing GetSystemPropertyUint32

Merged-In: I5a24533f2ce6d146e528661e7cf6b86008537f3f
(cherry picked from commit c4d022fc)
Change-Id: I074e35aecefe3f1f8fc1e95d1fd0401f99d57f55