DOC: Generate the charset tables dynamically from codes

[seisman]

Description of proposed changes

After adding the myst-nb extension in #3379, it's possible to generate the charset tables dynamically from codes.

Preview:

• This branch: https://pygmt-dev--3409.org.readthedocs.build/en/3409/techref/encodings.html
• Main branch: https://www.pygmt.org/dev/techref/encodings.html

Pros:

1. No need to maintain the charset tables manually
2. Make sure that the documentation is consistent with the codes

Cons:

1. Maybe a little slower in building the documentation [Building docs takes the same time (105 seconds) on the main branch and this PR, so the changes in this PR has negligible effects].
2. ruff can't format the codes in Markdown ☂️ Formatter: Support formatting of embedded code astral-sh/ruff#8237, so we need to format the codes manually.

[seisman]

This function is modified from the original script at #3206 (comment)

[seisman]

The default value is 'commonmark', which doesn't support tables.

[seisman]

Here is the CSS styles from myst-nb.

div.cell_output tr,
div.cell_output th,
div.cell_output td {
  text-align: right;
  vertical-align: middle;
  padding: 0.5em 0.5em;
  line-height: normal;
  white-space: normal;
  max-width: none;
  border: none;
}

The text-align is set to right, which makes sense for displaying objects like pandas.DataFrame (an example at https://myst-nb.readthedocs.io/en/latest/render/format_code_cells.html#remove-stdout-or-stderr).

In MyST, the table cell alignment can be controlled using : characters (https://myst-parser.readthedocs.io/en/latest/syntax/tables.html), which is done by assigning text-left/text-center/text-right to cells. These CSS classes are not defined in Sphinx_rtd_theme, so we have to define them here.