Add kernel per-uid cpu time reader tests to presubmit

Add TEST_MAPPING file to enable presubmit testing for changes to
KernelCpuUidTimeReader, KernelCpuUidBpfTimeReader and
KernelSingleUidTimeReader.

Test: atest
Bug: 138317993
Change-Id: Ic6272f101647a0e6fb3508b79c66387fefda0b04
Signed-off-by: Connor O'Brien <connoro@google.com>