Fix constructors and type parameters in the new lookup code

[jcollins-g]

This is a batch of small changes and accompanying tests that correct the following issues in the new lookup code:

• Finding TypeParameters was inappropriately logged as a non-equivalent result. Since they don't actually link to anything, it's not important that we found one when we didn't in the old code.
• The allowDefaultConstructors boolean was not set correctly now that we actually have parse nodes, this is now fixed.
• Ambiguity between requiring a callable and requiring a constructor is fixed in the new code; it works better than the old one did now.
• Consistently look up field formal parameters instead of doing so accidentally.
• All constructor lookups have been overhauled, with names appropriate for the new lookup system inserted in the referenceChildren tables.

[coveralls]

Coverage increased (+0.03%) to 57.658% when pulling d148222 on jcollins-g:constructor-lookup-fix into e5e596c on dart-lang:master.

[srawlins]

Looks great!