Negative values should not disappear. For example, if _HIWORD returns 63000,
then _GET_Y_LPARAM should return -2536, but now it returns 63000.
This fixes that.
context_windows.go is used for all the platforms. However, it used syscall.Syscall which behaves differently on macOS
and Windows as well as windows.BytePtrToString which isn't available on Linux or macOS.
This commit replaces syscall.Syscall with purego.SyscallN and windows.BytePtrToString with a copied version called
bytePtrToString.
Updates #2546
Many of the structs found in internal.h (internal_windows.go) contain defines such as GLFW_WIN32_WINDOW_STATE
which gets replaced with a struct defined in win32platform_windows.go (win32_platform.h).
Originally, these structs where directly placed inside of internal_windows.go. However, to make it easier to add macOS
and Linux these cannot be in this file.
This commit separates the windows specific structs into the respective windows file and updates the field to be named
state.
Updates #2546
