Support room-defined height as well

Much like widget widths, it is acceptable for us to forget what everyone's height was previously at.

src/hooks/useStateCallback.ts

@@ -0,0 +1,28 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import {Dispatch, SetStateAction, useState} from "react";
+
+// Hook to simplify interactions with a store-backed state values
+// Returns value and method to change the state value
+export const useStateCallback = <T>(initialValue: T, callback: (v: T) => void): [T, Dispatch<SetStateAction<T>>] => {
+    const [value, setValue] = useState(initialValue);
+    const interceptSetValue = (newVal: T) => {
+        setValue(newVal);
+        callback(newVal);
+    };
+    return [value, interceptSetValue];
+};