Implemented a HINSTANCE getter function for Windows (#1213)

* Expose HINSTANCE now using a getter function

* Missing changes

* remove unused import

* Required changes for the PR

* Rust fmt

* Use GetWindowLong

* Use GetWindowLong

src/platform_impl/windows/window.rs

@@ -14,7 +14,7 @@ use std::{
 use winapi::{
     ctypes::c_int,
     shared::{
-        minwindef::{DWORD, LPARAM, UINT, WORD, WPARAM},
+        minwindef::{DWORD, HINSTANCE, LPARAM, UINT, WORD, WPARAM},
         windef::{HWND, POINT, RECT},
     },
     um::{
@@ -358,6 +358,11 @@ impl Window {
         self.window.0
     }
 
+    #[inline]
+    pub fn hinstance(&self) -> HINSTANCE {
+        unsafe { winuser::GetWindowLongW(self.hwnd(), winuser::GWL_HINSTANCE) as *mut _ }
+    }
+
     #[inline]
     pub fn raw_window_handle(&self) -> RawWindowHandle {
         let handle = WindowsHandle {