This change adds a GN template to the pw_unit_test module which defines
a group of unit tests. The template creates a generated_file target with
JSON metadata for the unit tests and dependencies within the test group.
These metadata files are intended to be parsed by the test runner script
to run unit tests outside of GN.
A pw_test_group target is added to each of the existing modules which
have unit tests.
Change-Id: I363b937da365d0a3482a979feace18ecba1807a9