[ENHANCEMENT] Stop relying on arbitary code files in /thirdparty and use libiaries instead

from https://bugzilla.redhat.com/show_bug.cgi?id=2316282 Breakdown of the third_party stuff:

• aom/inc/aom: Used only in tests. Should be available in Fedora through aom 2. Delete if running the tests proves too hard, otherwise indicate in the SourceLicense breakdown or comments.
• aom_dsp: Same as above, but upstream does not seem to expose it.
• cpuinfo: Available in fedora build supports linking to it. Please delete it and use -DUSE_EXTERNAL_CPUINFO=ON.
• fastfeat: Dead project and there seems to be an alternative code-generated version 3. For now though, just Provides: bundled() it and include it's license.
• googletest: Available in Fedora. Needs some patching to remove the third_party/googletest references and replace them with find_package(GTest), target_link_libraries(GTest::gtest GTest::gtest_main) and a few other stuff. Alternatively open an issue and ask them to support linking against system gtest (or better have FetchContent(FIND_PACKAGE_ARGS) support).
• safestringlib: Available upstream project 4 but not packaged to Fedora. Please open an issue in either project to request supporting that.

In any case the license breakdown should indicate the third_party stuff, either inside the License field or SourceLicense field (for the case of googletest which is not packaged), and appropriate Provides: bundled() should be added.