[llvm] [llvm] Add API to get decompressed size of a zstd compressed buffer. (PR #107020)

[Fangrui Song via llvm-commits]

MaskRay wrote:

As an alternative, you might use `ZSTD_getFrameContentSize` within the to-be-upstreamed runtime. `lld/ELF/OutputSections.cpp` has an example using the advanced APIs as we are not yet comfortable exposing these in LLVMSupport.

https://github.com/llvm/llvm-project/pull/107020