fix(@angular-devkit/build-angular): add tslint as an optional peer dependency

tslint is currently used by the tslint builder within this package but is not represented in the dependencies. The can lead to accidental version mismatches as well as package manager hoisting problems due to the package manager not knowing the full dependency set of the package.

Author: clydin

packages/angular_devkit/build_angular/package.json

@@ -84,6 +84,7 @@
     "karma": "^5.2.0",
     "ng-packagr": "^10.0.0",
     "protractor": "^7.0.0",
+    "tslint": "^6.1.0",
     "typescript": ">=3.9 < 4.1"
   },
   "peerDependenciesMeta": {
@@ -98,6 +99,9 @@
     },
     "protractor": {
       "optional": true
+    },
+    "tslint": {
+      "optional": true
     }
   }
 }

packages/angular_devkit/build_angular/src/tslint/index.ts

@@ -11,7 +11,7 @@ import { readFileSync } from 'fs';
 import * as glob from 'glob';
 import { Minimatch } from 'minimatch';
 import * as path from 'path';
-import * as tslint from 'tslint'; // tslint:disable-line:no-implicit-dependencies
+import * as tslint from 'tslint';
 import { Program } from 'typescript';
 import { stripBom } from '../utils/strip-bom';
 import { Schema as RealTslintBuilderOptions } from './schema';
@@ -25,7 +25,7 @@ interface LintResult extends tslint.LintResult {
 async function _loadTslint() {
   let tslint;
   try {
-    tslint = await import('tslint'); // tslint:disable-line:no-implicit-dependencies
+    tslint = await import('tslint');
   } catch {
     throw new Error('Unable to find TSLint. Ensure TSLint is installed.');
   }