[SHELL32_APITEST] Extend ShellState API tests

- Skip registry tests if the key is missing, but keep testing
- Add tests for different bitmasks and compare amount of set bytes
- Add inter-process tests (using shell32_apitest_sub) that verify
  shell behavior, especially covering parts that were recently fixed
  in 4fecc90 (reactos#9293).

All tests are confirmed to pass on Windows 2003, Vista, 7, 8.1 and 10.

CORE-20585

Author: binarymaster