[jak2] More texture animations (#2831)

Added framework to do texture animations entirely in C++. Currently only
works on relatively simple ones, and doesn't handle updating all
parameters - only the speeds.

Connected texture animations to merc and tfrag for skull gems, dark
bomb, and scrolling conveyors.

Cleaned up Tfragment/Tfrag3, which used to be two classes. This was one
of the first C++ renderers, so it had a weird design.

common/custom_data/TFrag3Data.cpp

@@ -720,6 +720,9 @@ void Level::memory_usage(MemoryUsageTracker* tracker) const {
   for (const auto& texture : textures) {
     texture.memory_usage(tracker);
   }
+  for (const auto& texture : index_textures) {
+    texture.memory_usage(tracker);
+  }
   for (const auto& tftk : tfrag_trees) {
     for (const auto& tree : tftk) {
       tree.memory_usage(tracker);