[client] egl: make native HDR encoding-safe

Request true floating-point EGL configs for scRGB and expose the native
encodings supported by the selected surface. Fall back to software HDR
mapping when the surface cannot represent the incoming wire format.

Resample PQ in linear light, keep SDR-only effects out of native PQ
chains, and consume the cursor-specific white level without changing
binary monochrome cursor mask operations.

client/renderers/EGL/desktop.c

@@ -468,7 +468,8 @@ bool egl_desktopRender(EGL_Desktop * desktop, unsigned int outputWidth,
     egl_postProcessConfigModified(desktop->pp);
   if (processFrame &&
       egl_postProcessRun(desktop->pp, tex, desktop->mesh,
-        width, height, outputWidth, outputHeight, dma) &&
+        width, height, outputWidth, outputHeight, dma,
+        desktop->hdr && desktop->hdrPQ) &&
       egl_postProcessNeedsFullFrame(desktop->pp))
   {
     /* The filter output may have changed everywhere, but this only applies to