Problem:
Running :TOhtml with a file containing modeline may generate an invalid modeline in the output.

Solution:
Add `<!-- vim: set nomodeline: -->` to the output.
Use vi-compatible modeline format ("set foo:"), to avoid the trailing `-->` being treated as part of the modeline.

When a plugin registers a TermRequest handler there is currently no way
for the handler to know where the terminal's cursor position was when
the sequence was received. This is often useful information, e.g. for
OSC 133 sequences which are used to annotate shell prompts.

Modify the event data for the TermRequest autocommand to be a table
instead of just a string. The "sequence" field of the table contains the
sequence string and the "cursor" field contains the cursor
position when the sequence was received.

To maintain consistency between TermRequest and TermResponse (and to
future proof the latter), TermResponse's event data is also updated to
be a table with a "sequence" field.

BREAKING CHANGE: event data for TermRequest and TermResponse is now a
table

This updates the extmark namespace to search for when filtering out
semantic tokens to match the new namespace style recently introduced.

Font-family names must be enclosed in quotation marks to ensure that
fonts are applied correctly when there are spaces in the name.

Fix an issue where multiple fonts specified in `vim.o.guifont` are
inserted as a single element, treating them as a single font.

Support for escaping commas with backslash and ignoring spaces
after a comma.

ref `:help 'guifont'`

Problem:
Things like underlines are always given a default foreground highlight
regardless of the value of `sp`.

Solution:
Check for `sp` first, and apply that color to the text decoration color if it
exists.

Limitations:
If there is no value of `sp`, vim applies a text decoration color that matches
the foreground of the text. This is still not implemented (and seems like a much
more complex problem): in TOhtml, the underline will still be given a default
foreground highlight.

This mostly means replacing `nvim_buf_call` and `nvim_win_call` with
`vim._with`.