Implement improved overload candidates, aka "Bestest Betterness".#24756

Merged

gafter merged 5 commits intodotnet:features/compilerfrom gafter:better-candidates

Feb 20, 2018

+2,041-647

Commits on Feb 10, 2018

Implement improved overload candidates, aka "Bestest Betternes".
gafter
committed

Commits on Feb 12, 2018

Commits on Feb 13, 2018

Rename ConstraintFailureDiagnosticsOpt to ConstraintFailureDiagnostics
gafter
committed

Commits on Feb 16, 2018

Add tests suggested by @VSadov .
gafter
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