Add area_thresh to COMMON_OPTIONS

[michaelgrund]

Description of proposed changes

While working on #1423 I recognized that the -A alias already implemented in coast as area_thresh is also used in several other modules like grdlandmask, grdmath and gmtselect. This PR adds area_thresh to the common options list.

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.

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[seisman]

It sounds reasonable to me. Two thoughts:

1. Also update the area_thresh docstring of coast in this PR?
2. Although these options (e.g, area_thresh, cmap, pen) are used in many modules, they are not real common options. I think it's OK to list the common and "non-common" options in the same COMMON_OPTIONS dictionary, but it would be better to add a few comments explaining that the dictionary contains both common and non-common options, and it would be better to organize them in two groups (separated by a few comment lines). This could be done in a separate PR if agreed.

[seisman]

2. Although these options (e.g, area_thresh, cmap, pen) are used in many modules, they are not real common options. I think it's OK to list the common and "non-common" options in the same COMMON_OPTIONS dictionary, but it would be better to add a few comments explaining that the dictionary contains both common and non-common options, and it would be better to organize them in two groups (separated by a few comment lines). This could be done in a separate PR if agreed.

Or we can define two separate dicts (e.g., COMMON_OPTIONS and NONCOMMON_OPTIONS) and another dict that is the combination of both.

[michaelgrund]

It sounds reasonable to me. Two thoughts:

1. Also update the `area_thresh` docstring of `coast` in this PR?

Will do that!

2. Although these options (e.g, `area_thresh`, `cmap`, `pen`) are used in many modules, they are not real common options. I think it's OK to list the common and "non-common" options in the same `COMMON_OPTIONS` dictionary, but it would be better to add a few comments explaining that the dictionary contains both common and non-common options, and it would be better to organize them in two groups (separated by a few comment lines). This could be done in a separate PR if agreed.

I would go with this option @seisman. Maybe a good first issue to add some comments explaining that the dictionary contains both, common and non-common options?

[seisman]

Looks good to me.

[maxrjones]

Just missing one close bracket, otherwise looks good. Thanks!

[weiji14]

😀

[seisman]

I think this PR is ready to merge. Feel free to merge it when you have time @michaelgrund