[llvm] [Support] Add LLVMToolSession for in-process tool invocation (PR #221996)

[Anutosh Bhat via llvm-commits]

anutosh491 wrote:

> I reviewed the code and I like this abstraction.

That's awesome @rnk ;)

I'll try my best to address all the above reviews by today and hopefully we would be in a better position to take this in !

Then I would like some help from y'all on the clang driver change to inculate this design : https://github.com/llvm/llvm-project/pull/222531 

https://github.com/llvm/llvm-project/pull/221996