swift234

[AST] Make MemberRefExpr source range include start of implicit base expression if valid.

Change how MemberRefExpr and DynamicMemberRefExpr calculate their starting locations so
that even if their base expression is implicit, they will use its starting location if
that location is valid rather than falling back to the start of the name of the member.

Without this change, the Fix-It to suggest wrapping a nested member reference (where the
base is an implicit LoadExpr) in 'if #available(...)' would be inserted in the middle of
the expression.

rdar://problem/20662960

Swift SVN r27799