feat(common): rename underlying NgFor class and add a type parameter

[chuckjaz]

feat(compiler): generate a type parameters for generic type references
feat(tsc-wrapped): record arity of generic classes

Note, this affects the underlying class and should not affect usage.

DEPRECATION:

• the NgFor class is now deprecated. Use NgForOf<T> instead.
  IMPORTANT: Only the NgFor class is deprecated, not the ngFor
  directive. The *ngFor and related directives are unaffected by
  this change as references to the NgFor class generated from
  templates will be automatically converted to references to
  NgForOf<T> without requiring any template modifications.
• TrackByFn is now deprecated. Use TrackByFunction<T> instead.

Migration:

• Replace direct references to the NgFor class to NgForOf<any>.
• Replace references to TrackByFn to TrackByFunction<any>.

BREAKING CHANGE:
A definition of Iterable<T> is now required to correctly compile
Angular applications. Support for Iterable<T> is not required at
runtime but a type definition Iterable<T> must be available.

NgFor, and now NgForOf<T>, already supports Iterable<T> at
runtime. With this change the type definition is updated to reflect
this support.

Migration:

• add "es2015.iterable.ts" to your tsconfig.json "libs" fields.

What kind of change does this PR introduce? (check one with "x")

[x] Feature

What is the current behavior? (You can also link to an open issue here)

NgFor uses NgForRow for its context which has a $implicit type of any. The type of $implicit should be the element type of the iterator assigned to the ngForOf property.

The class name NgFor is incorrect as well as it implies it is associated with the ngFor directive instead of the ngForOf directive. Calling it NgFor seems to imply that if we add syntax to support iterating the fields of an object such as for...in, NgFor would need to host the code instead of creating a new class.

The TypeScript code generation does not supply the correct number of type arguments to classes with generic parameters.

What is the new behavior?

A new class is created, NgForOf<T> and the old class is deprecated and transformed into a derived class class NgFor extends NgForOf<any> {}.

The TypeScript emitter was changed to generate the correct number of type parameters for references to generic types.

The TypeScript code generation will generate NgForOf<any> for references to this class. However, once #12398 lands, the type parameter would be used to validate references to the context$implicit

Does this PR introduce a breaking change? (check one with "x")

[x] Yes
[ ] No

This change requires the project's tsconfig.json to include a definition of Iterable<T> to in the global scope. This can be accomplished by adding "es2015.iterable" into the "libs" field.

[vicb]

feat(compile): generate a type parameters for generic type references
feat(tsc-wrapped): record arity of generic classes

Should this be 2 separate commits ?

[chuckjaz]

Sure. Do you want three commits, one for adding arity, one for adding generics and one for renaming NgFor etc?

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