[llvm] [SPIR-V] Expose an API call to initialize SPIRV target and translate input LLVM IR module to SPIR-V (PR #107216)

[Vyacheslav Levytskyy via llvm-commits]

VyacheslavLevytskyy wrote:

@Keenuts Thank you for the insight and advices. I've tweaked the interface a bit to account for the fact that the list of extensions is one of the most frequently used command line argument with more complicated composition and parsing. After the latest change the list of extensions is an argument to the API call. What is your opinion about the change, does it look slightly better now?
CC: @michalpaszkowski 

https://github.com/llvm/llvm-project/pull/107216