Ensure plotting xarray grids with different central meridians work on some projections

[weiji14]

Description of proposed changes

Adds tests to make sure that plotting xarray.DataArray grids at different central meridians work properly for different projection types. See #515 (comment) for background context. Note that this depends on GMT >= 6.1.1 and won't work yet.

Reverts the runfirst workaround required in #476, reverts #531 grdtrack gallery example crash on macOS due to a problematic meridian setting.

Note that this PR may depend on #555 ✔️

Addresses #390, Fixes #515

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If adding new functionality, add an example to docstrings or tutorials.