For doing syntax highlighting with tree sitter, we're going to be

shipping many of the highlights files from the nvim-treesitter package.

These highlights files are often much, much better than the ones that

are shipped with the grammars themselves, but they do have a few things

that need to be worked around.
The most complicated of these is that neovim has custom lua-match? and

not-lua-match? predicates in its query implementation that allow

queries to use Lua pattern matching.
I initially implemented my own custom predicate that used the luapatt

library to handle these, but while that works, for extensive

highlighting, it involves performing huge numbers of function calls from

the C code in py-tree-sitter to the predicate callable, adding

significant overhead.
This change adds a function that can translate (most) Lua patterns to

Python regexes. To my knowledge, there are only two features of Lua

patterns which are not supported: the non-greedy *- operator, and the

balanced parentheses %b class. Neither of these is used anywhere in

any of the queries files that we need.

Ran unit tests.
Used this with processed queries to verify that queries that formerly

  used lua-match? worked correctly with the rewritten regexes.