feat(@angular/build): add dataurl, base64 loaders

[imirkin]

This passes through the existing esbuild functionality to support dataurl and base64 loaders, in addition to the pre-existing text, binary, and file loaders.

Both the dataurl and base64 loaders return strings with the relevant content. There is no way to control whether the dataurl method uses base64 or plain text encoding, and no way to control the mime type it detects.

Fixes #30391

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?

Currently only the text/binary/file esbuild loaders are usable.

Issue Number: #30391

What is the new behavior?

This adds the dataurl/base64 loaders as well.

Does this PR introduce a breaking change?

• Yes
• No

Other information

It wasn't clear to me how to cause the documentation at e.g. https://angular.dev/tools/cli/build-system-migration#file-extension-loader-customization to be updated. I updated the comments in schema.json.

[imirkin]

Let me know if you want me to fix the lint issue. Prettier wants some IMO questionable formatting:

  let loaderExtensions:
    | Record<string, 'text' | 'binary' | 'file' | 'dataurl' | 'base64'>
    | undefined;

and

      if (
        value !== 'text' &&
        value !== 'binary' &&
        value !== 'file' &&
        value !== 'dataurl' &&
        value !== 'base64' &&
        value !== 'empty'
      ) {
        continue;
      }

But if that's the project style, happy to include.

[dgp1130]

Thanks for the contribution, great addition to the CLI!