Add `SourceView` which doesn't own source text as base class of `Source` (#65309)
Summary:
This would save the cost copying text from stack to heap in some cases (like
parsing function schema during loading phase of libtorch.so)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65309
Reviewed By: swolchok
Differential Revision: D31060315
Pulled By: gmagogsfm
fbshipit-source-id: 0caf7a688b40df52bb4388c5191d1a42351d6f1a
