Add some quick-and-dirty debug info for TileStore (#2887)

* Add some quick-and-dirty debug info for TileStore

I'm still in need of more detailed data in order to understand why big layout shifts happen in large calls. This adds a developer option to enable logging and a visual indicator for the state of the TileStore. The indicator should be useful for matching up the behavior I'm seeing in my recordings with the right timestamps.

* Reduce performance impact of checking for whether debug mode is enabled

---------

Co-authored-by: Hugh Nimmo-Smith <hughns@element.io>

src/settings/DeveloperSettingsTab.tsx

@@ -12,6 +12,7 @@ import { FieldRow, InputField } from "../input/Input";
 import {
   useSetting,
   duplicateTiles as duplicateTilesSetting,
+  debugTileLayout as debugTileLayoutSetting,
 } from "./settings";
 import type { MatrixClient } from "matrix-js-sdk/src/client";
 
@@ -22,6 +23,9 @@ interface Props {
 export const DeveloperSettingsTab: FC<Props> = ({ client }) => {
   const { t } = useTranslation();
   const [duplicateTiles, setDuplicateTiles] = useSetting(duplicateTilesSetting);
+  const [debugTileLayout, setDebugTileLayout] = useSetting(
+    debugTileLayoutSetting,
+  );
 
   return (
     <>
@@ -70,6 +74,17 @@ export const DeveloperSettingsTab: FC<Props> = ({ client }) => {
           )}
         />
       </FieldRow>
+      <FieldRow>
+        <InputField
+          id="debugTileLayout"
+          type="checkbox"
+          checked={debugTileLayout}
+          label={t("developer_mode.debug_tile_layout_label")}
+          onChange={(event: ChangeEvent<HTMLInputElement>): void =>
+            setDebugTileLayout(event.target.checked)
+          }
+        />
+      </FieldRow>
     </>
   );
 };

src/settings/settings.ts

@@ -75,6 +75,8 @@ export const developerSettingsTab = new Setting(
 
 export const duplicateTiles = new Setting("duplicate-tiles", 0);
 
+export const debugTileLayout = new Setting("debug-tile-layout", false);
+
 export const audioInput = new Setting<string | undefined>(
   "audio-input",
   undefined,