Move symbols from the Cocoa SDK to its own Platform grammar file

This makes it easier to automatically update the grammar to new SDKs.
Update platform definitions to latest SDK
Remove script used to grep Cocoa headers for grammar symbols

This is no longer used, instead we used a libclang-based approach.
Include ‘source.c.platform#functions’ instead of redeclaring them
Remove legacy completion command (using dialog 1.x)
Don’t show “Completion: Inside @selector” in the bundle menu

This is consistent with the other two completion commands.
Remove legacy support files for documentation lookups
Update completion index (using 10.10 SDK)
Ignore Swift documentation matches for ⌃H

This avoids showing a pop-up menu for most documentation lookups.
Add methods from Cocoa protocols to our completion index
Completion was missing objc/NSObject.h and objc/runtime.h