feat(api): allow floats to be opened in non-current tabpage (#28480)

\

src/nvim/window.c

@@ -5127,7 +5127,14 @@ win_T *win_alloc(win_T *after, bool hidden)
   block_autocmds();
   // link the window in the window list
   if (!hidden) {
-    win_append(after, new_wp, NULL);
+    tabpage_T *tp = NULL;
+    if (after) {
+      tp = win_find_tabpage(after);
+      if (tp == curtab) {
+        tp = NULL;
+      }
+    }
+    win_append(after, new_wp, tp);
   }
 
   new_wp->w_wincol = 0;