Restructure frontend code to allow for extensions (#4721)

# Description of Changes
Move frontend code into `core` folder and add infrastructure for
`proprietary` folder to include premium, non-OSS features

frontend/src/core/utils/sidebarUtils.ts

@@ -0,0 +1,34 @@
+import { SidebarRefs, SidebarState, SidebarInfo } from '@app/types/sidebar';
+
+/**
+ * Gets the All tools sidebar information using React refs and state
+ * @param refs - Object containing refs to sidebar elements
+ * @param state - Current sidebar state
+ * @returns Object containing the sidebar rect and whether the tool panel is active
+ */
+export function getSidebarInfo(refs: SidebarRefs, state: SidebarState): SidebarInfo {
+  const { quickAccessRef, toolPanelRef } = refs;
+  const { sidebarsVisible, readerMode } = state;
+  
+  // Determine if tool panel should be active based on state
+  const isToolPanelActive = sidebarsVisible && !readerMode;
+  
+  let rect: DOMRect | null = null;
+  
+  if (isToolPanelActive && toolPanelRef.current) {
+    // Tool panel is expanded: use its rect
+    rect = toolPanelRef.current.getBoundingClientRect();
+  } else if (quickAccessRef.current) {
+    // Fall back to quick access bar
+    // This probably isn't needed but if we ever have tooltips or modals that need to be positioned relative to the quick access bar, we can use this
+    rect = quickAccessRef.current.getBoundingClientRect();
+  }
+  
+  return {
+    rect,
+    isToolPanelActive,
+    sidebarState: state
+  };
+}
+
+