Call XInitThreads first; XCloseDisplay cleanup

[RonaldZielaznicki]

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Closes #1290

Context

yppy provided some excellent advise on discord:

XInitThreads should be the first xlib function called (though im not sure i would believe in xlib multithreading...)

And after I mentioned an error code on exit, they also advised:

error 3 is badwindow
probably something is using it after XDestroyWindow

The discussion after lead to the realization that platform.deinit is called before the GPU backend is released. This caused a race condition where the GPU backend might interact with the window before it is released.

Changes

• change: libx11.XInitThreads is now called first when initializing X11.
• remove: X11's custom errorHandler in favor of the default handler's more verbose description.
• change: platform.deinit is now called after the GPU backend has been released.

Some additional detail

To show why I removed the custom X11 error handler.

Custom Error Message

err(mach): X11: error code 3

Default Error Message

X Error of failed request:  BadWindow (invalid Window parameter)
  Major opcode of failed request:  148 ()
  Minor opcode of failed request:  1
  Resource id in failed request:  0x5400002
  Serial number of failed request:  2035
  Current serial number in output stream:  2036

[slimsag]

I'd like us to remove this from the codebase ASAP, since we don't have any multi-threading yet this should be doing nothing :) so let's get it out and debug any issues that arise from removing it