Unify Int32ConstantEntry and NativeIntConstantEntry

[drcjt]

Instead of having separate classes unify into a single class representing integral constants. The class can easily determine the vartype and exact size based on the actual integral constant itself.

This is kind of like this PR from the real dotnet - dotnet/runtime#85951 - but here we have 16 bit and 32 bit constants whereas PR 85951 is dealing with 32 and 64 bit constants respectively.