UI: Rename search button variable

I landed D10527 in rB1a8aee0a7cec accidentally, and the version there was
missing a name change discussed in review. This commit just renames the
boolean variable controlling the special behavior for attribute search.

Original message meant for this change:
For geometry nodes we will use search buttons to display a list of
attributes available the last time the node tree was executed (D10519).
Because this list is just a hint, we need to be able to enter any string,
not just strings from the search items.

This patch adds a boolean option to string buttons to enable this.
The change is quite simple, changes to behavior are only required in
two places. The type-specific button struct changes help a lot here.

Differential Revision: https://developer.blender.org/D10527

source/blender/editors/interface/interface_handlers.c

@@ -3413,7 +3413,7 @@ static void ui_textedit_end(bContext *C, uiBut *but, uiHandleButtonData *data)
 
         if ((ui_searchbox_apply(but, data->searchbox) == false) &&
             (ui_searchbox_find_index(data->searchbox, but->editstr) == -1) &&
-            !but_search->all_strings_valid) {
+            !but_search->results_are_suggestions) {
           data->cancel = true;
 
           /* ensure menu (popup) too is closed! */