Cleanup: Reduce context usage in UI functions

Part of https://developer.blender.org/T74429.

There's a chance that this causes some issues becaue in some cases we
change from getting the window from context to getting it from somewhere
else.

source/blender/editors/include/UI_interface.h

@@ -632,7 +632,7 @@ void uiPupBlockOperator(struct bContext *C,
 
 void UI_popup_block_close(struct bContext *C, struct wmWindow *win, uiBlock *block);
 
-bool UI_popup_block_name_exists(struct bContext *C, const char *name);
+bool UI_popup_block_name_exists(const struct bScreen *screen, const char *name);
 
 /* Blocks
  *