MLIRSideEffects -> MLIRSideEffectInterfaces
SideEffects.h -> SideEffectInterfaces.h
SideEffects.cpp -> SideEffectInterface.cpp

Note that I haven't renamed TableGen/SideEffects.h or TableGen/SideEffects.cpp

find -name "*.h" -exec sed -i "s/SideEffects.h/SideEffectInterfaces.h/" "{}" \;
find -name "CMakeLists.txt" -exec sed -i "s/MLIRSideEffects/MLIRSideEffectInterfaces/" "{}" \;

Differential Revision: https://reviews.llvm.org/D79890