Add support for generic types in methods and as cast

[matanlurey]

Closes dart-lang/tools#902
Closes dart-lang/tools#903

Sorry for the extra breaking changes - but even while updating the tests I found these confusing - and would rather fix now before we have too many users in a stable branch:

1.0.0-beta+3

• Added support for genericTypes parameter for ExpressionBuilder#invoke:

expect(
  explicitThis.invoke('doThing', [literal(true)], genericTypes: [
    lib$core.bool,
  ]),
  equalsSource(r'''
    this.doThing<bool>(true)
  '''),
);

• Added a castAs method to ExpressionBuilder:

expect(
  literal(1.0).castAs(lib$core.num),
  equalsSource(r'''
    1.0 as num
  '''),
);

BREAKING CHANGES

• Removed namedNewInstance and namedConstInstance, replaced with name: :

expect(
  reference('Foo').newInstance([], name: 'other'),
  equalsSource(r'''
    new Foo.other()
  '''),
);

• Renamed named parameter to namedArguments:

expect(
  reference('doThing').call(
    [literal(true)],
    namedArguments: {
      'otherFlag': literal(false),
    },
  ),
  equalsSource(r'''
    doThing(true, otherFlag: false)
  '''),
);

[natebosch]

what do you think about 'constructor' instead of 'name' for the argument?

[matanlurey]

Liked it! Done.

[natebosch]

LGTM