fix: rewrite .js to .ts imports in test files (re-apply)

Re-apply .ts import rewrites to test files after they were lost
in a previous git checkout operation. Also fix bare package
specifiers that had erroneous .ts extension.

Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bennypowers

packages/test-runner-junit-reporter/test/junitReporter.test.ts

@@ -4,8 +4,8 @@ import { promises as fs } from 'fs';
 import path from 'path';
 import globby from 'globby';
 
-import { chromeLauncher } from '@web/test-runner-chrome.ts';
-import type { TestRunnerCoreConfig } from '@web/test-runner-core.ts';
+import { chromeLauncher } from '@web/test-runner-chrome';
+import type { TestRunnerCoreConfig } from '@web/test-runner-core';
 import { runTests } from '@web/test-runner-core/test-helpers.ts';
 import { junitReporter } from '../src/junitReporter.ts';