[llvm] [CAS] Add LLVMCAS library with InMemoryCAS implementation (PR #114096)

[Steven Wu via llvm-commits]

cachemeifyoucan wrote:

Most content in this PR has been split into following stacked PR:
* [CAS] Add LLVMCAS library with InMemoryCAS implementation https://github.com/llvm/llvm-project/pull/114096
* [CAS] Add ActionCache to LLVMCAS Library https://github.com/llvm/llvm-project/pull/114097
* [FileSystem] Allow exclusive file lock https://github.com/llvm/llvm-project/pull/114098
* [CAS] Add MappedFileRegionBumpPtr https://github.com/llvm/llvm-project/pull/114099
* [CAS] Add OnDiskHashMappedTrie https://github.com/llvm/llvm-project/pull/114100
* [CAS] Add OnDiskGraphDB and OnDiskKeyValueDB https://github.com/llvm/llvm-project/pull/114102
* [CAS] Add OnDiskCAS https://github.com/llvm/llvm-project/pull/114103
* [CAS] Add llvm-cas tools to inspect on-disk LLVMCAS https://github.com/llvm/llvm-project/pull/114104

Going to close this PR once everything is moved. Please head to the new PRs for easier review. Thanks.

https://github.com/llvm/llvm-project/pull/114096