Move more path logic for tests to testing.cc, so it can be used without
depending on CommonArtTest.

Preparation to fix the libart-gtest dependency in
art_standalone_libartpalette_tests.

Due to a new #include, this necessitated fixing a bunch of `testing`
namespace references that could become ambigious wrt `art::testing`.

Test: m generate-boot-image
Test: art/tools/buildbot-build.sh
Bug: 404306250
Change-Id: Iafb3d73148125775c9c5ddbcbaef39dc61859118
48 files changed