Details:
Currently doing 4 system calls per WM_INPUT message, which can cause the thread handling the message loop to be swapped out several times:
* GetProp - to get window data from the window handle
* GetRawInputData - to retrieve the raw input data
* 2 calls to GetMessageExtraInfo - to ignore synthetic mouse events generated for touchscreens
In this change:
* Replaced GetProp by iterating the list of windows maintained by SDL (with a fallback to GetProp). Note that this will affect all messages and not just WM_INPUT
* only calling GetMessageExtraInfo if a touchscreen has been detected
Fix for https://jira.valve.org/browse/CSGO-4855
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