feat(@angular/build): support postcss js config

[BBboy01]

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• 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)
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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?

executor: @angular-devkit/build-angular:dev-server

Users can use customized postcss config, but json only, have a lot of limitions.

Issue Number: #27819

What is the new behavior?

Users can use js config file(.js, .cjs and .mjs), it not only can handle all situations of json config, but also more powerful.

And the postcss early migration guide still recommend to use js as configuration file.

Does this PR introduce a breaking change?

• Yes
• No

Not support json configuration again. Try support json or ts will increase the complexity of code bases.

Other information