Add experimentalImportFactories when migrating to loadChildren import syntax

[filipesilva]

The #14181 migration also needs to add "experimentalImportFactories": true to angular.json (#13948) to make the import syntax supported in VE.

The tsconfig file should also be updated to use "module": "esnext", and a e2e test should be added to test the update works and an app with lazy routes will be updated and runs properly.

[filipesilva]

Part of this is done in #14222

[alexeagle]

We should add this in the same migration with fix-lazy-routes so if we drop that feature from RC, we also drop the addition of this "experimental" flag

[alexeagle]

Don't need this one if we do #14231

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