This fixes an issue where a value would hide the type.
```
export interface Foo {
someMethod(): void;
}
export const Foo: Function = ...;
```
In the above example the `Foo` constant will hide the `interface Foo` symbol.
This change properly saves the interface in addition to the type.
PR Close#27223
Also use it to test the public API for core and common
Once we have an ng_package for every package, we can remove
the npm dependency on ts-api-guardian and the gulp-based
public api check.
PR Close#22544
Joey Perrott
Miško Hevery
Alex Eagle