jak3: speedrunner mode (#3761)

Base implementation of the popup menu and speedrunner mode in Jak 3.
Autosplitter is untested because I'm on Linux.

Also a couple of other misc changes:

- Model replacements can now have custom bone weights. Needs the "Use
Custom Bone Weights" property (provided by the OpenGOAL Blender plugin)
enabled in Blender.
- Better error message for lump syntax errors in custom level JSON
files.

goal_src/jak3/kernel/gstring.gc

@@ -815,8 +815,18 @@
 
 (define *temp-string* (new 'global 'string 2048 (the-as string #f)))
 
+;; og:preserve-this
+(define *temp-string2* (new 'global 'string 2048 (the string #f)))
+
+(defconstant EMPTY_STRING "")
+
 (#when PC_PORT (define *pc-encoded-temp-string* (new 'global 'string 2048 (the-as string #f))))
 
+(#when PC_PORT
+  (define *pc-cpp-temp-string*
+    "A convenient place to retrieve a string from C++"
+    (new 'global 'string 2048 (the string #f))))
+
 (kmemclose)
 
 (defmacro string-format (&rest args)