[MLIR][LLVM] Add `llvm.experimental.constrained.fptrunc` operation (#86260)

Add operation mapping to the LLVM
`llvm.experimental.constrained.fptrunc.*` intrinsic.

The new operation implements the new
`LLVM::FPExceptionBehaviorOpInterface` and
`LLVM::RoundingModeOpInterface` interfaces.

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Signed-off-by: Victor Perez <victor.perez@codeplay.com>