Figure.coast: Improve documentation

[yvonnefroehlich]

Description of proposed changes

Some improvements of the documentation of Figure.coast:

• Use bullet point lists
• Remove the clipping and dumping options to avoid confusions, as the functionality is not available or currently under development; please see the related issue Figure.coast: No output of "+l|L" of "dcw" parameter ("E") when using an IDE #2646, and PRs Add clip parameter to pygmt.Figure.coast #1706 (, and Wrap clip #1779).

Preview: https://pygmt-dev--3325.org.readthedocs.build/en/3325/api/generated/pygmt.Figure.coast.html

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 wrapping a new module, open a 'Wrap new GMT module' issue and submit reasonably-sized PRs.
• If adding new functionality, add an example to docstrings or tutorials.
• Use underscores (not hyphens) in names of Python files and directories.

Slash Commands

You can write slash commands (/command) in the first line of a comment to perform
specific operations. Supported slash command is:

• /format: automatically format and lint the code