swift234

Adding a separate method for visiting subscript references in SourceEntityWalker.

When SourceEntityWalker visits a subscript reference it sometimes needed to visit
both open and close brackets. It used to be implemented as two calls to a regular
visitDeclReference which confused the clients expecting one call per a reference, 
for example indexing was recording two references to a subscript.

We add a separate visitSubscriptReference to resolve this problem.



Swift SVN r31494