feat(custom-webpack): add extract-i18n builder

[just-jeb]

PR Checklist

Please check if your PR fulfills the following requirements:

• 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
[x] 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: closes #659

What is the new behavior?

A new extract-i18n builder is available in @angular-builders/custom-webpack thus supporting custom extraction flows.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[autoapproval]

Approved 👍