swift

3e4a9d86 - [overlay] Fix Foundation extensions to Substring

[overlay] Fix Foundation extensions to Substring When a substring gets bridged to NSString, it loses the initial offset, therefore APIs that accept or return StringIndex ranges should handle this case explicitly by adding/subtracting the substring start offset. Fixes <rdar://problem/33873277> (cherry picked from commit 7322b63c4495e3b32f8197fd26307f948f7b3148)