swift234

SE-0064 / SR-1239: Code completion for #selector of property getters/setters.

Implement basic code completion support for #selector with property
getters/setters. The vast majority of this implementation comes from
Alex Hoppen (@ahoppen), with only a handful of my own tweaks. Alex has
more interesting ideas on improving this that I wasn't quite ready to
commit to, so this is more basic than the overall goal.