feat(diff): infer treesitter filetype highlights from filename

[mmfallacy]

PR Description

This PR infers the filetype from the corresponding file's path. That is,

• diff.lua M.render() function takes in file as a parameter (lua table).
• This file parameter is from difftastic's (via the lib) JSON output, which is a list of files with the following properties:
  • file.additions;
  • file.aligned_Lines;
  • file.language;

  This is what we currently use for setting file types where we lookup a const table.

  • file.path;

  This is the path which contains the filename including the extension vim can use to infer filetypes.

  • ...
• When the lookup fails, we use filename from file.path to infer the filetype via vim.filetype.match.
• Pass this to ensure_treesitter like before.

More tangibly, without modifying the lookup table
Before:

After:

Related Issues

This may essentially close #16 for filetypes that aren't yet handled.