[MLIR][LLVM] Copy byval attributes during inlining.

Support inlining of function calls with the byval attribute on function
arguments by copying the pointee into a newly alloca'ed pointer at the
callsite before inlining.

The alignment attribute is not yet taken into account.

Reviewed By: ftynse, gysit

Differential Revision: https://reviews.llvm.org/D146616