This patch is a continuation of D11695 but this patch is independent.
Blender need to tell the input method program where the conversion candidate window is during Japanese and Chinese input.
In macOS, there are displays where the window size and the native pixel size are different, so the candidate window may appear in an unnatural position.
This patch converts the cursor position x and y for matching macOS window coordinate.
On Windows, GHOST_GetNativePixelSize returns 1, so it has no effect.