[llvm] [VPlanPatternMatch] Introduce m_ConstantInt (PR #159558)

[Luke Lau via llvm-commits]

https://github.com/lukel97 approved this pull request.

Not sure if we will ever need to match and capture an APInt in VPlan but I guess this mirrors PatternMatch.h.

https://github.com/llvm/llvm-project/pull/159558