Handle Unicode input in xrdp keyboard driver

[YTjungle666]

Summary

• Handle xrdp's WM_UNICODE_INPUT backend event in the xorgxrdp keyboard driver.
• Map Unicode codepoints onto a rotating range of scratch keycodes and post normal X key events, so existing X clients receive text through the native X input path.
• Preserve existing scancode keyboard handling while adding temporary Shift handling for ASCII uppercase/lowercase text sent as Unicode.
• Avoid scratch keycodes that carry modifier, IME or special keypad behavior in the default XKB map.

This is intended to support Chinese text input and pasted Unicode text from Microsoft Remote Desktop mobile clients and Apache Guacamole browser sessions, while keeping existing keyboard behavior working.

Companion xrdp PR: neutrinolabs/xrdp#3804

Testing

• Built with the companion xrdp branch and installed the resulting 0.10.80 local build on Debian.
• Ran make check for xorgxrdp.
• Replayed captured Microsoft Remote Desktop mobile and Apache Guacamole input samples against the installed Xorg modules. The replay matched 83/83 expected text codepoints, covering direct Chinese input, pasted Chinese text, Chinese punctuation, lowercase ASCII, uppercase ASCII, and symbols.