Begin porting matmul test suite from iree-org/iree.

[ScottTodd]

Progress on #2.

This begins to port the tests from https://github.com/iree-org/iree/tree/main/tests/e2e/matmul. The changes here aim to be minimal, but a lot of cleanup is needed to make this sustainable.

• A new CMake project named iree-test-suites-matmul is added. We could share this with other test suites that need CMake, or let each test suite create its own. I don't want to overgeneralize yet while so much is still up in the air.
• The CMake project depends on the IREE runtime libraries and header files to build a iree-e2e-matmul-test binary. This binary handles preparing inputs, running a compiled program, and comparing outputs against a reference implementation. That may be split into multiple libraries or parts of it may move into Python or another test harness. TBD.
• The CMake project then defines some test cases using iree_generated_e2e_runner_test. This may be split into an offline generation step and a test runner other than ctest. TBD.

TODO:

• Fix namespace/symbol collisions in test_utils.h (fork further) and include it correctly
• Fix namespace/symbol collisions in iree_e2e_generated_runner_test.cmake (fork further)
• Add a GitHub Actions workflow running the tests
• Structure the CMake project such that it can be used from iree-org/iree in place of the current tests
• Fork or remove dependencies on the upstream CMake helpers used by matmul/iree_e2e_generated_runner_test.cmake?
• Allow pointing at a local IREE, like https://github.com/ScottTodd/iree/tree/infra-e2e-test-suites which deletes the in-tree tests and supporting infra

[erman-gurses]

Thanks, Scott, LGTM!