Add "test-only" flag for cc modules

As part of aosp/3022586 where we added the idea of "test-only" modules
and top_level_test_targets, this CL implements that for cc_ modules.

We let users set "test-only" on cc_library, but not on other modules
where the module kind is implicitly test-only, like cc_test.
Here the implementation, not the user decides it is test-only.

% gqui from  "flatten(~/aosp-main-with-phones/out/soong/ownership/all_teams.pb, teams)" proto team.proto:AllTeams 'select teams.kind, count(*) where teams.top_level_target = true group by teams.kind'                    aosp_shiba[6:15:47]/0
+--------------+----------+
|  teams.kind  | count(*) |
+--------------+----------+
| art_cc_test  |       56 |
| cc_benchmark |       68 |
| cc_fuzz      |      515 |
| cc_test      |     3518 |
| cc_test_host |        6 |
+--------------+----------+

 % gqui from  "flatten(~/aosp-main-with-phones/out/soong/ownership/all_teams.pb, teams)" proto team.proto:AllTeams 'select teams.kind, count(*) where teams.test_only = true group by teams.kind'                           aosp_shiba[6:16:26]/0
+--------------------------+----------+
|        teams.kind        | count(*) |
+--------------------------+----------+
| art_cc_test              |       56 |
| art_cc_test_library      |       13 |
| cc_benchmark             |       68 |
| cc_fuzz                  |      515 |
| cc_test                  |     3518 |
| cc_test_host             |        6 |
| cc_test_library          |      484 |
+--------------------------+----------+

Bug: b/327280661

Test: m nothing --no-skip-soong-tests
Test: go test ./cc
Test: m all_teams
Change-Id: I344436c424a9dfbdcf27e10f42f5cebc3d2b1261