GUAC-584: Add basic handling for Unicode text - just stubs, no converting to UTF-8 yet.
GUAC-584: Handle Unicode data (STUB). Need real conversion code with actual length calculations.
GUAC-584: Add iconv-style function in common. Stub implementation and test.
GUAC-584: Implement UTF8 read and write. Add basic identity test.
GUAC-584: Implement UTF16. Clean up tests.
GUAC-584: Simplify copy logic. Store clipboard in static 256K buffer. Convert from UTF16 properly.