refactor(@angular-devkit/schematics): remove `UpdateBuffer` and rename `UpdateBuffer2` to `UpdateBuffer`

[kyubisation]

This PR removes the internally built UpdateBuffer and renames UpdateBuffer2 (based on magic-string) to UpdateBuffer. This should have little to no impact for consumers.

BREAKING CHANGE: The depracated UpdateBuffer has been removed and UpdateBuffer2 is renamed to UpdateBuffer. With this change the related and deprecated symbols ContentCannotBeRemovedException and Chunk have also been removed.

PR Checklist

Please check to confirm your PR fulfills the following requirements:

• [x] The commit message follows our guidelines: https://github.com/angular/angular-cli/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• [x] Tests for the changes have been added (for bug fixes / features)
• [x] 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)
• [x] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [ ] Documentation content changes
• [ ] Other... Please describe:

What is the current behavior?

The deprecated UpdateBuffer instance is being used per default.

Issue Number: N/A

What is the new behavior?

The magic-string based UpdateBuffer2 is being used per default.

Does this PR introduce a breaking change?

• [x] Yes
• [ ] No

Other information

See #21209, #21110, #24035 and #24044 Re-created PR as advised: https://github.com/angular/angular-cli/pull/24044#issuecomment-1305988693