Fix FPS menu in "Format" panel not following translation setting

The FPS menu was using a cached value which wasn't being refreshed
when translation changed.

Add `bpy.app.handlers.translation_update_post` handler which runs
when translation changes, this can be used to clear any cached UI
values.

Ref !117049

source/blender/python/intern/bpy_app_handlers.cc

@@ -90,6 +90,7 @@ static PyStructSequence_Field app_cb_info_fields[] = {
     {"composite_cancel", "on a compositing background job (cancel)"},
     {"animation_playback_pre", "on starting animation playback"},
     {"animation_playback_post", "on ending animation playback"},
+    {"translation_update_post", "on translation settings update"},
     /* NOTE(@ideasman42): This avoids bad-level calls into BPY API
      * but should not be considered part of the public Python API.
      * If there is a compelling reason to make these public, the leading `_` can be removed. */