HWUI: Turn on Skia tracing by default

This can provide useful information when diagnosing jank. It also
introduces a little bit of overhead, which is why we haven't turned it
on before. That said, the overhead is only relevant during tracing.

Bug: 221813628
Test: perfetto
Change-Id: I311d902797e0b9ecf53631f2f9f2df6cf4860635