Select required sub-modules of a git dependency

[kvark]

When cargo sees a git dependency, it fetches all the submodules - https://github.com/gfx-rs/wgpu/pull/1903/checks?check_run_id=3508714595#step:5:9

Describe the problem you are trying to solve
This can take minutes of CI time, which is a waste if these submodules aren't really needed.

Describe the solution you'd like

foo  = { git = "https://foo.com/foo", submodules = ["x", "y"] }

Notes
Related to gfx-rs/wgpu#1903

[ehuss]

Thanks for the request! I think this is a duplicate of #4247 (and #7987 to a lesser extent), so closing in favor of that.

[kvark]

Oh great! I did look for the duplicates and somehow missed these.