Add remaps for copy, move and deref operators

[hermann-noll]

This PR adds remapped operator names for the copy, move and dereference operators. Previously this would have produced invalid C# code (e.g. public unsafe void operator=(. Unfortunately I could not find much guidance for "canonical C#" names, so "MoveFrom", "CopyFrom" and "Access" (for ->) might not be the best choice.

Note that I did not use return types for the tests as this seems to be its own bug with returning references (e.g. C++ MyStruct& abc() { return *this; } would produce C# MyStruct* abc() { return *this; }.