fix(@schematics/angular): change extends from tsconfig.base.json to tsconfig.json

[alan-agius4]

Closes: #18534

[Splaktar]

Based on what I observed in #18534 (comment), I'm not sure that this is sufficient.

I still had comments in my tsconfig.json about it being a "Solution Style" tsconfig.json file and the contents of my tsconfig.base.json got deleted but not moved into my tsconfig.json.

[alan-agius4]

@Splaktar, it's because we where using the wrong JsonFile instance here: https://github.com/angular/angular-cli/pull/18540/files#diff-d1380d3bc19bb56c82d31f1222da33ecL63

This should solve that issue as well.

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