[llvm] [NFC][llvm-ir2vec] llvm_ir2vec.cpp breakup to extract a reusable header for IR2VecTool, and MIR2VecTool classes (PR #172304)

[Nishant Sachdeva via llvm-commits]

https://github.com/nishant-sachdeva edited https://github.com/llvm/llvm-project/pull/172304