fix: Use SVG icon assets (#9569)

core/css.ts

@@ -461,7 +461,7 @@ input[type=number] {
 }
 
 .blocklyMenuItemSelected .blocklyMenuItemCheckbox {
-  background: url(<<<PATH>>>/sprites.png) no-repeat -48px -16px;
+  background: url(<<<PATH>>>/sprites.svg) no-repeat -48px -16px;
   float: left;
   margin-left: -24px;
   position: static;  /* Scroll with the menu. */

core/sprites.ts

@@ -11,5 +11,5 @@
 export const SPRITE = {
   width: 96,
   height: 124,
-  url: 'sprites.png',
+  url: 'sprites.svg',
 };

core/toolbox/category.ts

@@ -692,7 +692,7 @@ Css.register(`
 }
 
 .blocklyToolboxCategoryIcon {
-  background-image: url(<<<PATH>>>/sprites.png);
+  background-image: url(<<<PATH>>>/sprites.svg);
   height: 16px;
   vertical-align: middle;
   visibility: hidden;