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.

modules/markup/sanitizer_default_test.go

@@ -62,6 +62,10 @@ func TestSanitizer(t *testing.T) {
 		`<a href="javascript:alert('xss')">bad</a>`, `bad`,
 		`<a href="vbscript:no">bad</a>`, `bad`,
 		`<a href="data:1234">bad</a>`, `bad`,
+
+		// Some classes and attributes are used by the frontend framework and will execute JS code, so make sure they are removed
+		`<div class="link-action" data-attr-class="foo" data-url="xxx">txt</div>`, `<div data-attr-class="foo">txt</div>`,
+		`<div class="form-fetch-action" data-markdown-generated-content="bar" data-global-init="a" data-global-click="b">txt</div>`, `<div data-markdown-generated-content="bar">txt</div>`,
 	}
 
 	for i := 0; i < len(testCases); i += 2 {