docs: Automatically generate documentation from goal_src code (#2214)

This automatically generates documentation from goal_src docstrings,
think doxygen/java-docs/rust docs/etc. It mostly supports everything
already, but here are the following things that aren't yet complete:
- file descriptions
- high-level documentation to go along with this (think pure markdown
docs describing overall systems that would be co-located in goal_src for
organizational purposes)
- enums
- states
- std-lib functions (all have empty strings right now for docs anyway)

The job of the new `gen-docs` function is solely to generate a bunch of
JSON data which should give you everything you need to generate some
decent documentation (outputting markdown/html/pdf/etc). It is not it's
responsibility to do that nice formatting -- this is by design to
intentionally delegate that responsibility elsewhere. Side-note, this is
about 12-15MB of minified json for jak 2 so far :)

In our normal "goal_src has changed" action -- we will generate this
data, and the website can download it -- use the information to generate
the documentation at build time -- and it will be included in the site.
Likewise, if we wanted to include docs along with releases for offline
viewing, we could do so in a similar fashion (just write a formatting
script to generate said documentation).

Lastly this work somewhat paves the way for doing more interesting
things in the LSP like:
- whats the docstring for this symbol?
- autocompleting function arguments
- type checking function arguments
- where is this symbol defined?
- etc

Fixes #2215

common/util/string_util.h

@@ -19,4 +19,5 @@ std::string diff(const std::string& lhs, const std::string& rhs);
 /// Default splits on \n characters
 std::vector<std::string> split(const ::std::string& str, char delimiter = '\n');
 std::string join(const std::vector<std::string>& strs, const std::string& join_with);
+std::vector<std::string> regex_get_capture_groups(const std::string& str, const std::string& regex);
 }  // namespace str_util