Previously we were using an anonymous type `{specifier: string; qualifier: string;}`
throughout the code base. This commit gives this type a name and ensures it
is only defined in one place.

The `getDeclaration()` function now searches down into the AST for
matching nodes, which is needed for UMD testing.

In UMD formats, imports are always namespaced. This commit makes
ngcc more tolerant of such structures.

This will be important for UMD support.

Previously these fake files were full TypeScript source
files (`.ts`) but this is not necessary as we only need the
typings not the implementation.

In some cases the `forwardRef` helper has been imported via a namespace,
e.g. `core.forwardRef(...)`.

This commit adds support for unwrapping such namespaced imports when
ngtsc is statically evaluating code.

Previously the same `Renderer` was used to render typings (.d.ts)
files. But the new `UmdRenderer` is not able to render typings files
correctly.

This commit splits out the typings rendering from the src rendering.
To achieve this the previous renderers have been refactored from
sub-classes of the abstract `Renderer` class to  classes that implement
the `RenderingFormatter` interface, which are then passed to the
`Renderer` and `DtsRenderer` to modify its rendering behaviour.

Along the way a few utility interfaces and classes have been moved
around and renamed for clarity.

The dependency resolution that works out the order in which
to process entry-points must also understand UMD formats.

Previously we were relying upon the `.get()` method to return `undefined`
but it is clearer and safer to always check with `.has()` first.