implement eq for literal

[0xalpharush]

Fixes #1286
IR generated after this PR:

Contract Setter
        Function Setter.set(uint256[1],uint256,uint256) (*)
                Expression: self[key] = value
                IRs:
                        REF_0(uint256) -> self[key]
                        REF_0 (->self) := value(uint256)
Contract SetterTest
        Function SetterTest.f(uint256,uint256) (*)
                Expression: params.set(key,value)
                IRs:
                        LIBRARY_CALL, dest:Setter, function:Setter.set(uint256[1],uint256,uint256), arguments:['params', 'key', 'value']