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.
Problem: :TOhtml doesn't properly handle virtual text when it has
multiple highlight groups. It also improperly calculates position offset
for multi-byte virt_text characters.
Solution: Apply the `vim.api.nvim_strwidth` broadly to properly
calculate character offset, and handle the cases where the `hl` argument
can be a table of multiple hl groups.
Specifically, functions that are run in the context of the test runner
are put in module `test/testutil.lua` while the functions that are run
in the context of the test session are put in
`test/functional/testnvim.lua`.
Closes https://github.com/neovim/neovim/issues/27004.
