Mark frame info structs with rb_gc_mark_movable

Using rb_gc_mark_movable and a reference update function, we can make
frame infos movable in memory, and avoid pinning frame info backtraces.

```
require "objspace"
exceptions = []
GC.disable
50_000.times do
  begin
    raise "some exception"
  rescue => exception
    exception.backtrace_locations
    exceptions << exception
  end
end
GC.enable
GC.compact
p ObjectSpace.dump_all(output: :string).lines.grep(/"pinned":true/).count
```

Co-authored-by: Peter Zhu <peter@peterzhu.ca>

vm_backtrace.c

@@ -134,7 +134,14 @@ static void
 location_mark(void *ptr)
 {
     struct valued_frame_info *vfi = (struct valued_frame_info *)ptr;
-    rb_gc_mark(vfi->btobj);
+    rb_gc_mark_movable(vfi->btobj);
+}
+
+static void
+location_ref_update(void *ptr)
+{
+    struct valued_frame_info *vfi = ptr;
+    vfi->btobj = rb_gc_location(vfi->btobj);
 }
 
 static void
@@ -150,6 +157,7 @@ static const rb_data_type_t location_data_type = {
         location_mark,
         RUBY_TYPED_DEFAULT_FREE,
         NULL, // No external memory to report,
+        location_ref_update,
     },
     0, 0, RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED | RUBY_TYPED_EMBEDDABLE
 };