feat(@angular-devkit/build-angular): expose built-in karma config

[nicojs]

PR Checklist

Please check to confirm your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular-cli/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Issue Number: #24294

What is the new behavior?

Expose the build-in karma config to anyone that wants to use it.

// karma.conf.js
const setDefaultConfig = require('@angular-devkit/build-angular/src/builders/karma/karma.conf.js');
module.exports = function(config) {
 setDefaultConfig(config);
 config.set({
   // my own custom overrides
 });
}

Does this PR introduce a breaking change?

• Yes
• No

Other information

[alan-agius4]

Thanks for your contribution. But this has been superseded by #24458

[angular-automatic-lock-bot]

This issue has been automatically locked due to inactivity.
Please file a new issue if you are encountering a similar or related problem.

Read more about our automatic conversation locking policy.

_{This action has been performed automatically by a bot.}