Two Linux startup blockers:
1. Skia's Interface::new_native() dlopens libGL/GLX, which fails on
the EGL contexts this project always creates on Linux — GL init
errored and the app exited (the tracked LINUX_GPU_SKIA_LOADER_TBD
gap). GlContextProvider now exposes gl_proc_address; the glutin
provider resolves through its display (eglGetProcAddress on EGL)
and SharedSkiaContext builds the interface via new_load_with,
falling back to new_native for providers without a loader. The
Linux GPU smoke tests are un-ignored (they soft-skip without a
working EGL stack unless STEP1A_REQUIRE_GPU=1).
2. Dropping casement's default features also dropped wayland-dlopen,
making libwayland-client a DT_NEEDED hard dependency — the binary
could not even load on X11-only hosts. Restore the feature so
libwayland loads at runtime when present.
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