Merge conflict in sdl and glfw keycodes.

From emscripten-core#22864

Author: sbc100

src/library_glfw.js

@@ -422,7 +422,7 @@ var LibraryGLFW = {
       // Prevent default backspace and tab behavior when the target 
       // is not an input or textarea. Otherwise, no text in the site can be deleted.
       if (event.target.tagName !== "INPUT" && event.target.tagName !== "TEXTAREA" &&
-        (event.keyCode === 8 /* backspace */ || event.keyCode === 9 /* tab */)) {
+        (event.key == 'Backspace' || event.key == 'Tab')) {
         event.preventDefault();
       }
     },

src/library_sdl.js

@@ -700,7 +700,7 @@ var LibrarySDL = {
           // is not an input or textarea. Otherwise, no text in the site can be deleted.
           if (event.type !== 'keydown' ||
               (!SDL.unicode && !SDL.textInput) ||
-              ((event.keyCode === 8 /* backspace */ || event.keyCode === 9 /* tab */ ) &&
+              ((event.key == 'Backspace' || event.key == 'Tab') &&
                   event.target.tagName !== "INPUT" && event.target.tagName !== "TEXTAREA")) {
               event.preventDefault();
           }