Refactor global init code and add more comments (#33755)

Follow up #33748

Now there are 3 "global" functions:

* registerGlobalSelectorFunc: for all elements matching the selector, eg: `.ui.dropdown`
* registerGlobalInitFunc: for `data-global-init="initInputAutoFocusEnd"`
* registerGlobalEventFunc: for `data-global-click="onCommentReactionButtonClick"`


And introduce `initGlobalInput` to replace old `initAutoFocusEnd` and
`attachDirAuto`, use `data-global-init` to replace fragile
`.js-autofocus-end` selector.

Another benefit is that by the new approach, no matter how many times
`registerGlobalInitFunc` is called, we only need to do one
"querySelectorAll" in the last step, it could slightly improve the
performance.

web_src/js/modules/init.ts

@@ -0,0 +1,26 @@
+export class InitPerformanceTracer {
+  results: {name: string, dur: number}[] = [];
+  recordCall(name: string, func: ()=>void) {
+    const start = performance.now();
+    func();
+    this.results.push({name, dur: performance.now() - start});
+  }
+  printResults() {
+    this.results = this.results.sort((a, b) => b.dur - a.dur);
+    for (let i = 0; i < 20 && i < this.results.length; i++) {
+      console.info(`performance trace: ${this.results[i].name} ${this.results[i].dur.toFixed(3)}`);
+    }
+  }
+}
+
+export function callInitFunctions(functions: (() => any)[]): InitPerformanceTracer | null {
+  // Start performance trace by accessing a URL by "https://localhost/?_ui_performance_trace=1" or "https://localhost/?key=value&_ui_performance_trace=1"
+  // It is a quick check, no side effect so no need to do slow URL parsing.
+  const perfTracer = !window.location.search.includes('_ui_performance_trace=1') ? null : new InitPerformanceTracer();
+  if (perfTracer) {
+    for (const func of functions) perfTracer.recordCall(func.name, func);
+  } else {
+    for (const func of functions) func();
+  }
+  return perfTracer;
+}