--dynamic-subtest support via testlists

Since 0b1de531 we support passing --dynamic-subtest when executing a test binary to limit the dynamic subsubtests we execute only to the ones matching the pattern. Runner is capable of parsing the result (since 21f30a48) but there is no way of getting them filter/executed via testlist.

Proposed notation:

igt@binary_name@subtests@dynamic

IMO we should not support this in any way when listing --list-subtests or listing/executing via the runner cmd line - this is meant as a "special case" for developers doing limited execution and wanting to get the results as .json - we should avoid using this for proper CI/automation.

Related: kernel self-tests and its "subtests".

Requested-by: @kdec5, @dtmrzgl
Cc: @emusial, @adrinael