[llvm] [llvm lib] `DataExtractor`: Add `StringOffsetSize` field and `getStringOffset()` (PR #190005)

[Greg Clayton via llvm-commits]

https://github.com/clayborg commented:

It seems like there are DataExtractor patches to remove getAddress() and other things. I am not sure llvm wants this in their DataExtractor? I am fine with it, but this might conflict with the recent direction of DataExtractor. Part of the motivation for this was for GSYM, and now the GSYM patch has DataExtractorGSYM, so we can move this there?

https://github.com/llvm/llvm-project/pull/190005