Fix 3066 glfw get cursor pos

This is the fix commit for #3066.

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1. fix `glfwGetCursorPos`(GLFW3 API):
    -  parameter type from 'i32' to 'double'.
2. add `GLFW.getMousePos`:
    - `i32` version for GLFW2.
3. fix `glfwGetMousePos`(GLFW2 API):
    - from call `GLFW.getCursorPos` to call `GLFW.getMousePos`