Add build target for prebuilt trace_processor_shell only

Some tests wish to use the trace_processor_shell, but not use the trace
configs from prebuilts. Currently the perfetto_artifacts target includes
both of these, so including it could cause collisions between the
prebuilt trace configs and custom configs in a test repo. Add a target
to allow including the trace_processor_shell only.

Note, including the ToT trace_processor_shell from external/perfetto is
not currently possible due to b/335313600.

Bug: 354634358
Test: Run `atest DtsExamplePowerTest` together with ag/29172347

Change-Id: I97e1d43a4914df3e6a254aa62a823602e754c815