Fix Caps Lock and Backspace mapping for Colemak

(cherry picked from commit 906ad64d7be6facee85bdf08f6f890dc8c8c1bca)

src/video/windows/SDL_windowsevents.c

@@ -137,6 +137,11 @@ static SDL_Scancode VKeytoScancodeFallback(WPARAM vkey)
 static SDL_Scancode VKeytoScancode(WPARAM vkey)
 {
     switch (vkey) {
+    case VK_BACK:
+        return SDL_SCANCODE_BACKSPACE;
+    case VK_CAPITAL:
+        return SDL_SCANCODE_CAPSLOCK;
+
     case VK_MODECHANGE:
         return SDL_SCANCODE_MODE;
     case VK_SELECT: