JANITORIAL: Add missing references to const function parameters

[mikrosk]

Applied to all const Common:: and const Graphics:: instances.

The biggest performance win is surely Common::String and Common::Path.

It also uncovered a few inconsistencies where a .h had a const parameter while its .cpp didn't.

[bluegr]

Nice work, thanks!

[lephilousophe]

It seems you switched to references enum types and pointer types.
For such types there will be a useless in direction.

[mikrosk]

@lephilousophe good point. I have reverted changes for

• Common::CodePage
• Common::EventType
• Common::Keycode
• Common::Language
• Common::Platform

in my local branch. However I'm not sure about Common::ArchiveMemberPtr: SO suggests passing by const reference in case of shared_ptr and older C++ standard: https://stackoverflow.com/a/8741626. AFAIR we officially support C++11, i.e. shared_ptr's move semantics still isn't a thing?