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.cpp

@@ -81,4 +81,16 @@ std::string diff(const std::string& lhs, const std::string& rhs) {
 std::vector<std::string> split(const ::std::string& str, char delimiter) {
   return google_diff::split_string(str, delimiter);
 }
+
+std::vector<std::string> regex_get_capture_groups(const std::string& str,
+                                                  const std::string& regex) {
+  std::vector<std::string> groups;
+  std::smatch matches;
+  if (std::regex_search(str, matches, std::regex(regex))) {
+    for (size_t i = 1; i < matches.size(); i++) {
+      groups.push_back(matches[i].str());
+    }
+  }
+  return groups;
+}
 }  // namespace str_util