Convert PDFBug, in web/debugger.js, to a class with static methods

This gets rid of one more closure from the code-base.

web/debugger.js

@@ -491,13 +491,14 @@ const Stats = (function Stats() {
 })();
 
 // Manages all the debugging tools.
-const PDFBug = (function PDFBugClosure() {
-  const buttons = [];
-  let activePanel = null;
+class PDFBug {
+  static #buttons = [];
 
-  return {
-    tools: [FontInspector, StepperManager, Stats],
-    enable(ids) {
+  static #activePanel = null;
+
+  static tools = [FontInspector, StepperManager, Stats];
+
+  static enable(ids) {
     const all = ids.length === 1 && ids[0] === "all";
     const tools = this.tools;
     for (const tool of tools) {
@@ -515,8 +516,9 @@ const PDFBug = (function PDFBugClosure() {
         return indexA - indexB;
       });
     }
-    },
-    init(container, ids) {
+  }
+
+  static init(container, ids) {
     this.loadCSS();
     this.enable(ids);
     /*
@@ -562,11 +564,12 @@ const PDFBug = (function PDFBugClosure() {
           `${tool.name} is disabled. To enable add "${tool.id}" to ` +
           "the pdfBug parameter and refresh (separate multiple by commas).";
       }
-        buttons.push(panelButton);
+      this.#buttons.push(panelButton);
     }
     this.selectPanel(0);
-    },
-    loadCSS() {
+  }
+
+  static loadCSS() {
     const { url } = import.meta;
 
     const link = document.createElement("link");
@@ -574,31 +577,32 @@ const PDFBug = (function PDFBugClosure() {
     link.href = url.replace(/.js$/, ".css");
 
     document.head.append(link);
-    },
-    cleanup() {
+  }
+
+  static cleanup() {
     for (const tool of this.tools) {
       if (tool.enabled) {
         tool.cleanup();
       }
     }
-    },
-    selectPanel(index) {
+  }
+
+  static selectPanel(index) {
     if (typeof index !== "number") {
       index = this.tools.indexOf(index);
     }
-      if (index === activePanel) {
+    if (index === this.#activePanel) {
       return;
     }
-      activePanel = index;
+    this.#activePanel = index;
     for (const [j, tool] of this.tools.entries()) {
       const isActive = j === index;
-        buttons[j].classList.toggle("active", isActive);
+      this.#buttons[j].classList.toggle("active", isActive);
       tool.active = isActive;
       tool.panel.hidden = !isActive;
     }
-    },
-  };
-})();
+  }
+}
 
 globalThis.FontInspector = FontInspector;
 globalThis.StepperManager = StepperManager;