refactor(@angular/build): provide karma runner for unit-test builder

The `runner` option for the `unit-test` builder can now be set to `karma`.
This leverages the existing `karma` builder for test execution. The `karma`
build related options are derived from the provided `buildTarget` option
instead of being manually specified within the `unit-test` builder. In
other areas, the test execution is the same with the exceptions of specifying
either a custom configuration file and/or a custom main file.

Author: clydin

packages/angular/build/src/builders/unit-test/builder.ts

@@ -21,6 +21,7 @@ import { ResultKind } from '../application/results';
 import { OutputHashing } from '../application/schema';
 import { writeTestFiles } from '../karma/application_builder';
 import { findTests, getTestEntrypoints } from '../karma/find-tests';
+import { useKarmaBuilder } from './karma-bridge';
 import { normalizeOptions } from './options';
 import type { Schema as UnitTestOptions } from './schema';
 
@@ -51,6 +52,14 @@ export async function* execute(
   const normalizedOptions = await normalizeOptions(context, projectName, options);
   const { projectSourceRoot, workspaceRoot, runnerName } = normalizedOptions;
 
+  // Translate options and use karma builder directly if specified
+  if (runnerName === 'karma') {
+    const karmaBridge = await useKarmaBuilder(context, normalizedOptions);
+    yield* karmaBridge;
+
+    return;
+  }
+
   if (runnerName !== 'vitest') {
     context.logger.error('Unknown test runner: ' + runnerName);
 

packages/angular/build/src/builders/unit-test/schema.json

@@ -16,7 +16,7 @@
     "runner": {
       "type": "string",
       "description": "The name of the test runner to use for test execution.",
-      "enum": ["vitest"]
+      "enum": ["karma", "vitest"]
     },
     "include": {
       "type": "array",