Add eslint type assertions rule

Fixes #3359

addons/xterm-addon-serialize/test/SerializeAddon.api.ts

@@ -487,9 +487,9 @@ function newArray<T>(initial: T | ((index: number) => T), count: number): T[] {
   const array: T[] = new Array<T>(count);
   for (let i = 0; i < array.length; i++) {
     if (typeof initial === 'function') {
-      array[i] = (<(index: number) => T>initial)(i);
+      array[i] = (initial as (index: number) => T)(i);
     } else {
-      array[i] = <T>initial;
+      array[i] = initial as T;
     }
   }
   return array;

addons/xterm-addon-webgl/src/WebglAddon.ts

@@ -24,9 +24,9 @@ export class WebglAddon implements ITerminalAddon {
       throw new Error('Cannot activate WebglAddon before Terminal.open');
     }
     this._terminal = terminal;
-    const renderService: IRenderService = (<any>terminal)._core._renderService;
-    const characterJoinerService: ICharacterJoinerService = (<any>terminal)._core._characterJoinerService;
-    const colors: IColorSet = (<any>terminal)._core._colorManager.colors;
+    const renderService: IRenderService = (terminal as any)._core._renderService;
+    const characterJoinerService: ICharacterJoinerService = (terminal as any)._core._characterJoinerService;
+    const colors: IColorSet = (terminal as any)._core._colorManager.colors;
     this._renderer = new WebglRenderer(terminal, colors, characterJoinerService, this._preserveDrawingBuffer);
     this._renderer.onContextLoss(() => this._onContextLoss.fire());
     renderService.setRenderer(this._renderer);