During elementwise fusion the fillOp's value was directly referred without casting which can create mismatching dtypes. Reviewed By: mravishankar, ThomasRaoux Differential Revision: https://reviews.llvm.org/D137447
Suggested by @lattner in https://discourse.llvm.org/t/rfc-define-precise-arith-semantics/65507/22. Tested with: `ninja check-mlir check-mlir-integration check-mlir-mlir-spirv-cpu-runner check-mlir-mlir-vulkan-runner check-mlir-examples` and `bazel build --config=generic_clang @llvm-project//mlir:all`. Reviewed By: lattner, Mogball, rriddle, jpienaar, mehdi_amini Differential Revision: https://reviews.llvm.org/D134762
