Refactor markup package (#32399)

To make the markup package easier to maintain:
1. Split some go files into small files
2. Use a shared util.NopCloser, remove duplicate code
3. Remove unused functions

modules/markup/html_email.go

@@ -0,0 +1,21 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package markup
+
+import "golang.org/x/net/html"
+
+// emailAddressProcessor replaces raw email addresses with a mailto: link.
+func emailAddressProcessor(ctx *RenderContext, node *html.Node) {
+	next := node.NextSibling
+	for node != nil && node != next {
+		m := emailRegex.FindStringSubmatchIndex(node.Data)
+		if m == nil {
+			return
+		}
+
+		mail := node.Data[m[2]:m[3]]
+		replaceContent(node, m[2], m[3], createLink("mailto:"+mail, mail, "mailto"))
+		node = node.NextSibling.NextSibling
+	}
+}