fix(@angular-devkit/build-angular): only import karma when running karma builder

Karma is an optional peer dependency, but with the recent changes we broke this as we imported karma outside of the execution method, which made this package to be always imported even when the Karma builder was not invoked.

(cherry picked from commit 5954d24)

Author: alan-agius4

goldens/public-api/angular_devkit/build_angular/index.md

@@ -7,7 +7,7 @@
 import { BuilderContext } from '@angular-devkit/architect';
 import { BuilderOutput } from '@angular-devkit/architect';
 import { BuildResult } from '@angular-devkit/build-webpack';
-import { ConfigOptions } from 'karma';
+import type { ConfigOptions } from 'karma';
 import { Configuration } from 'webpack';
 import { DevServerBuildOutput } from '@angular-devkit/build-webpack';
 import { Observable } from 'rxjs';

packages/angular_devkit/build_angular/src/builders/karma/index.ts

@@ -8,7 +8,7 @@
 
 import { BuilderContext, BuilderOutput, createBuilder } from '@angular-devkit/architect';
 import { strings } from '@angular-devkit/core';
-import { Config, ConfigOptions, config, constants } from 'karma';
+import type { Config, ConfigOptions } from 'karma';
 import { createRequire } from 'module';
 import * as path from 'path';
 import { Observable, from } from 'rxjs';
@@ -96,7 +96,7 @@ export function execute(
 
       const karmaOptions: KarmaConfigOptions = options.karmaConfig
         ? {}
-        : getBuiltInKarmaConfig(context.workspaceRoot, projectName);
+        : getBuiltInKarmaConfig(karma, context.workspaceRoot, projectName);
 
       karmaOptions.singleRun = singleRun;
 
@@ -145,7 +145,7 @@ export function execute(
         logger: context.logger,
       };
 
-      const parsedKarmaConfig = await config.parseConfig(
+      const parsedKarmaConfig = await karma.config.parseConfig(
         options.karmaConfig && path.resolve(context.workspaceRoot, options.karmaConfig),
         transforms.karmaOptions ? transforms.karmaOptions(karmaOptions) : karmaOptions,
         { promiseConfig: true, throwErrors: true },
@@ -184,6 +184,7 @@ export function execute(
 }
 
 function getBuiltInKarmaConfig(
+  karma: typeof import('karma'),
   workspaceRoot: string,
   projectName: string,
 ): ConfigOptions & Record<string, unknown> {
@@ -218,7 +219,7 @@ function getBuiltInKarmaConfig(
     reporters: ['progress', 'kjhtml'],
     port: 9876,
     colors: true,
-    logLevel: constants.LOG_INFO,
+    logLevel: karma.constants.LOG_INFO,
     autoWatch: true,
     browsers: ['Chrome'],
     restartOnFileChange: true,