fix(@schematics/angular): exclusively list the files in tsconfigs

[alan-agius4]

With the omission of includes or files in tsconfig files tsc will pick up all the files under the rootDir and make them as part of the compilation. In certain cases, redundant files will be picked up which will cause a slower compilations.

Related to: TOOL-949

[filipesilva]

Very comprehensive PR, great work!

[clydin]

I think this should only be enabled on new Ivy projects. New VE projects can still use string-based routes and this will break them.

[filipesilva]

Indeed they can, but it is deprecated. Ivy supports the string syntax as well currently. We decoupled the two things.

Maybe we should only do this in v9 then? Or perhaps we need to document in https://angular.io/guide/deprecations#loadchildren-string-syntax that if you want to use the string syntax you need to add the file to the files array.

[alan-agius4]

IMHO, I think an update to the docs should suffice.

[alan-agius4]

Make this for Ivy for the time being. And make this the default in version 9.

[alan-agius4]

The VE, part might be needed if we go with #15061 (comment)

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