Implement constructor tearoffs support in AngularDart

[eernstg]

This issue tracks support of the constructor tearoffs feature. See the enclosing meta-issue for details.

[devoncarew]

@grouma - did you find out if there was work to do here before this lands internally? Work that we'd like to do after it lands? We expect constructor tearoffs to be feature complete early October.

[grouma]

I discussed with the team internally. I don't think there is work to do besides verifying the feature. I just now was able to manually verify the feature works as expected for some edge cases the team was concerned about. We should be good from the Angular perspective unless something unforeseen pops up.

[devoncarew]

Great, thanks! I'll close - we can re-open more specific items if we do find issues.