Such injectables were not appearing in the providers lists of their NgModule.
This commit updates the doc-gen to support associating these automatically.
Further, it also allows developers to mark other injectables that are provided
in an NgModule with a reference to the NgModule where they are provided.
The commit also does a refactoring of the `processNgModuleDocs` dgeni
processor code, to make it easier to maintain.
Fixes#41203
PR Close#41960
