fix(xmake): compile GLFW Wayland backend on Linux

[Tenire]

What

• Hook wayland-scanner protocol code generation and compile Wayland backend sources (wl_init.c, wl_monitor.c, wl_window.c) into eui_glfw on Linux.
• Maintain dual-backend support (_GLFW_WAYLAND + _GLFW_X11) with graceful fallback to X11-only if Wayland development packages are absent.

Why

• The vendored GLFW xmake target previously only compiled X11 sources (x11_*.c) with _GLFW_X11, preventing applications from running natively under Wayland compositors and forcing them into XWayland.

How

• In eui_glfw's on_load, probe for wayland-scanner, wayland-client, and xkbcommon.
• If found, generate protocol headers and code from 3rd/glfw/deps/wayland/*.xml into target:autogendir(), add _GLFW_WAYLAND, append Wayland source files, and link client libraries.
• If not found, retain the default X11-only build.

Rationale & Reference

• Upstream GLFW 3.4 CMake parity: Matches 3rd/glfw/src/CMakeLists.txt (lines 66–107), which generates protocol headers from 3rd/glfw/deps/wayland/*.xml using wayland-scanner (client-header and private-code) and enables both Wayland and X11 by default.
• Self-contained in tree: The 9 protocol XML files are already bundled in 3rd/glfw/deps/wayland/.
• Runtime multi-backend selection: GLFW 3.4 dynamically detects WAYLAND_DISPLAY at glfwInit() and prefers native Wayland while dynamically loading client libraries via dlopen.
• Zero regression on non-Wayland setups: When wayland-scanner or Wayland packages are missing, the target silently falls back to pure X11 without failing configuration or compilation.