For the case of Clojure and other Lisp syntax highlighting, it is
necessary to create huge regexps consisting of hundreds of symbols with
the pipe (|) character. To make things more difficult, these Lisp
symbols sometimes consists of special characters that are themselves
part of special regexp characters like '*'. In addition to being
difficult to maintain, it's performance is suboptimal.

This patch introduces a new predicate to perform 'source' matching in
amortized constant time. This is accomplished by compiling a hash table
on the first use.

Fixes the following bug:
```
test/functional/helpers.lua:107: Error executing lua:
vim/treesitter/query.lua:256: attempt to index a nil value
```

feat(treesitter): allow injections to be configured through directives