This allows to overwrite templates for JIT and AOT components alike.
In contrast to `TestBed.overrideTemplate`, the template is compiled
in the context of the testing module, allowing to use other testing
directives.
Closes#19815
Before, as soon as a user called `TestBed.overrideProvider` for a provider
of a `NgModule` that was imported via `TestBed.configureTestingModule`,
that `NgModule` became lazy.
This commit changes this behavior to keep the `NgModule` eager,
with or without a call to `TestBed.overrideProvider`.
PR Close#19624
Tobias Bosch
Miško Hevery
Jason Aden