[flang][driver] Add support for `-fget-symbols-sources`

Adds support for `-fget-symbols-sources` in the new Flang driver. All
relevant tests are updated to use the new driver when
`FLANG_BUILD_NEW_DRIVER` is set.

`RUN` lines in tests are updated so `-fsyntax-only`
comes before `-fget-symbols-sources`. That's because:
  * both `-fsyntax-only` and `-fget-symbols-sources` are
    action flags, and
  * the new driver, flang-new, will only consider the right-most
    action flag.
In other words, this change is needed so that the tests work with both
`f18` (requires both flags) and `flang-new` (only considers the last
action flag).

Differential Revision: https://reviews.llvm.org/D98191