Add API to clear canvas renderer texture atlas

Fixes #3455

src/browser/public/Terminal.ts

@@ -222,6 +222,9 @@ export class Terminal implements ITerminalApi {
   public reset(): void {
     this._core.reset();
   }
+  public clearTextureAtlas(): void {
+    this._core.clearTextureAtlas();
+  }
   public loadAddon(addon: ITerminalAddon): void {
     return this._addonManager.loadAddon(this, addon);
   }