GridCore: add methods to HeaderPanel to add/remove toolbar items#33118

anna-shakhova wants to merge 6 commits intoDevExpress:26_1DevExpress/DevExtreme:26_1from

anna-shakhova:26_1__header_panel_add_remove_itemanna-shakhova/DevExtreme:26_1__header_panel_add_remove_itemCopy head branch name to clipboard