idmap2: improve Android.bp

Improve Android.bp in a few ways:

  - add cc_defaults
  - remove the tidy_flag "-warnings-as-errors=*"

A note on warnings-as-errors: the default set of tidy checks are
inherited from the lists in build/soong/cc/config/tidy.go. This set is
modified by the local Android.bp's tidy_checks. If a new check is
enabled as default, and idmap2 specifies warnings-as-errors, idmap2 will
potentially break the build. In light of this, keep warnings as
warnings.

Also add a few non-default tidy checks. This version of idmap2 doesn't
compile cleanly: fixes will come in future CLs.

Also exempt the auto-generated code from IIdmap2.aidl from clang-tidy by
containing it in a separate cc_library_static block.

Bug: 120024673
Test: mmm frameworks/base/cmds/idmap2
Change-Id: I589fce792075a44a77b79117aa16b63ef0bec142