[llvm] [CAS] Split on-disk CAS validate-if-needed into validation and recovery (PR #226291)

[Dmitry Vasilyev via llvm-commits]

slydiman wrote:

I have tested this patch on Windows. I didn't encounter this issue #226844.
But `llvm-cas.exe --cas any-non-existent-path --validate-if-needed` silently initializes a new DB and reports `validated successfully`. It confuses.

https://github.com/llvm/llvm-project/pull/226291