Fix CPU core locked to 100% on Linux X11/Wayland when idle (#1103)

The desktop event loop's `select()` call was watching stdin (file descriptor 0)
which acts as ALWAYS readable whenever stdin is redirected to /dev/null
or similar.
So taht was causing the loop to falsely run every time that the select
call was made, even if nothing actually was readable on any of those FDs.

The fix is to just ... not do that, haha. Only makepad-studio uses
something like that, but no longer. It now uses websockets only.

Also, harden vsync behavior by setting `eglSwapInterval` explicitly
(vsync on by default; MAKEPAD_NO_VSYNC opt-out) to ensure that things
that get continuously drawn are capped at the display's refresh rate.