map_interval: Add interval allocator and drop hack

Drop the std::list hack to allocate memory indefinitely.

Instead use a custom allocator that keeps references valid until
destruction. This allocates fixed chunks of memory and puts pointers in
a free list. When an allocation is no longer used put it back to the
free list, this doesn't heap allocate because std::vector doesn't change
the capacity. If the free list is empty, allocate a new chunk.

src/video_core/CMakeLists.txt

@@ -1,6 +1,7 @@
 add_library(video_core STATIC
     buffer_cache/buffer_block.h
     buffer_cache/buffer_cache.h
+    buffer_cache/map_interval.cpp
     buffer_cache/map_interval.h
     dirty_flags.cpp
     dirty_flags.h