Log chosen RenderPipelineType when running hwui_unit_tests

There are a few ways to run hwui_unit_tests: copy the binary to the
device and execute it directly, run with atest, tradefed, etc(?). Some
of these approaches have arcane ways of passing arguments down into the
executable, such as the `--renderer` flag. Logging what is actually
observed/chosen can help confirm that the flag is being passed
correctly.

Bug: b/338077634
Test: observed logs for `hwui_unit_tests --renderer=skiavk`
Flag: TEST_ONLY
Change-Id: I1a4e72fb08dedf36f9095b3844e346ffeefac602