Refactor: UI: Use regular button callbacks for curve, color ramp templates

Previously these used a special "menu func" that used an argument value
passed through each menu button's a2 value. This was more complex than
necessary given the existence of generic button callbacks.

So use std::function in these remaining cases, and remove the now-unused
`butm_func` and `butm_func_arg` values in the uiBlock.

source/blender/editors/include/UI_interface_c.hh

@@ -1689,7 +1689,6 @@ void UI_but_number_slider_precision_set(uiBut *but, float precision);
 void UI_but_search_preview_grid_size_set(uiBut *but, int rows, int cols);
 
 void UI_block_func_handle_set(uiBlock *block, uiBlockHandleFunc func, void *arg);
-void UI_block_func_butmenu_set(uiBlock *block, uiMenuHandleFunc func, void *arg);
 void UI_block_func_set(uiBlock *block, uiButHandleFunc func, void *arg1, void *arg2);
 void UI_block_funcN_set(uiBlock *block, uiButHandleNFunc funcN, void *argN, void *arg2);
 

source/blender/editors/interface/interface.cc

@@ -5840,12 +5840,6 @@ void UI_block_func_handle_set(uiBlock *block, uiBlockHandleFunc func, void *arg)
   block->handle_func_arg = arg;
 }
 
-void UI_block_func_butmenu_set(uiBlock *block, uiMenuHandleFunc func, void *arg)
-{
-  block->butm_func = func;
-  block->butm_func_arg = arg;
-}
-
 void UI_block_func_set(uiBlock *block, uiButHandleFunc func, void *arg1, void *arg2)
 {
   block->func = func;

source/blender/editors/interface/interface_handlers.cc

@@ -479,10 +479,6 @@ struct uiAfterFunc {
   void *handle_func_arg;
   int retval;
 
-  uiMenuHandleFunc butm_func;
-  void *butm_func_arg;
-  int a2;
-
   wmOperator *popup_op;
   wmOperatorType *optype;
   wmOperatorCallContext opcontext;
@@ -810,9 +806,7 @@ static void popup_check(bContext *C, wmOperator *op)
 static bool ui_afterfunc_check(const uiBlock *block, const uiBut *but)
 {
   return (but->func || but->apply_func || but->funcN || but->rename_func || but->optype ||
-          but->rnaprop || block->handle_func ||
-          (but->type == UI_BTYPE_BUT_MENU && block->butm_func) ||
-          (block->handle && block->handle->popup_op));
+          but->rnaprop || block->handle_func || (block->handle && block->handle->popup_op));
 }
 
 /**
@@ -853,12 +847,6 @@ static void ui_apply_but_func(bContext *C, uiBut *but)
   after->handle_func_arg = block->handle_func_arg;
   after->retval = but->retval;
 
-  if (but->type == UI_BTYPE_BUT_MENU) {
-    after->butm_func = block->butm_func;
-    after->butm_func_arg = block->butm_func_arg;
-    after->a2 = but->a2;
-  }
-
   if (block->handle) {
     after->popup_op = block->handle->popup_op;
   }
@@ -1067,9 +1055,6 @@ static void ui_apply_but_funcs_after(bContext *C)
     if (after.handle_func) {
       after.handle_func(C, after.handle_func_arg, after.retval);
     }
-    if (after.butm_func) {
-      after.butm_func(C, after.butm_func_arg, after.a2);
-    }
 
     if (after.rename_func) {
       after.rename_func(C, after.rename_arg1, static_cast<char *>(after.rename_orig));

source/blender/editors/interface/interface_intern.hh

@@ -561,9 +561,6 @@ struct uiBlock {
   uiButHandleNFunc funcN;
   void *func_argN;
 
-  uiMenuHandleFunc butm_func;
-  void *butm_func_arg;
-
   uiBlockHandleFunc handle_func;
   void *handle_func_arg;