feat(arch): implemented icon registration

packages/mermaid/src/rendering-util/svgRegister.ts

@@ -0,0 +1,33 @@
+import { Selection } from "d3-selection";
+
+type IconResolver =  (parent: Selection<SVGGElement, unknown, Element | null, unknown>) => Selection<SVGGElement, unknown, Element | null, unknown>
+type IconLibrary = Record<string, IconResolver>
+
+const icons: IconLibrary = {}
+
+const isIconNameInUse = (name: string): boolean => {
+    return icons[name] !== undefined;
+}
+
+const registerIcon = (name: string, resolver: IconResolver) => {
+    if(!isIconNameInUse(name)) {
+        icons[name] = resolver;
+    }
+}
+
+const registerIcons = (library: IconLibrary) => {
+    Object.entries(library).forEach(([name, resolver]) => {
+        if (!isIconNameInUse(name)) {
+            icons[name] = resolver;
+        }
+    })
+}
+
+const getIcon = (name: string): IconResolver | null => {
+    if (isIconNameInUse(name)) {
+        return icons[name];
+    }
+    return null; // TODO: return default
+}
+
+export { registerIcon, registerIcons, getIcon, isIconNameInUse, IconLibrary }