Instantiate LogMessage::CopyToEncodedBuffer separately for literals and non-literals to save an instruction at each operator<<(string) callsite.

The operator<<s get inlined at the callsite.  The saved instruction is a 'load immediate' to put the StringType argument in a register for passing.

This does make the logging TU slightly larger, but it will be an overall size win for all but the smallest programs.  Smaller, faster code at callsites is worth it anyway.

PiperOrigin-RevId: 528569773
Change-Id: Id8185266a975a12ab6f1a553c2c0846261822396