Refactor markup render system (#32533)

Remove unmaintainable sanitizer rules. No need to add special "class"
regexp rules anymore, use RenderInternal.SafeAttr instead, more details
(and examples) are in the tests

modules/htmlutil/html.go

@@ -0,0 +1,48 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package htmlutil
+
+import (
+	"fmt"
+	"html/template"
+	"slices"
+)
+
+// ParseSizeAndClass get size and class from string with default values
+// If present, "others" expects the new size first and then the classes to use
+func ParseSizeAndClass(defaultSize int, defaultClass string, others ...any) (int, string) {
+	size := defaultSize
+	if len(others) >= 1 {
+		if v, ok := others[0].(int); ok && v != 0 {
+			size = v
+		}
+	}
+	class := defaultClass
+	if len(others) >= 2 {
+		if v, ok := others[1].(string); ok && v != "" {
+			if class != "" {
+				class += " "
+			}
+			class += v
+		}
+	}
+	return size, class
+}
+
+func HTMLFormat(s string, rawArgs ...any) template.HTML {
+	args := slices.Clone(rawArgs)
+	for i, v := range args {
+		switch v := v.(type) {
+		case nil, bool, int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, float32, float64, template.HTML:
+			// for most basic types (including template.HTML which is safe), just do nothing and use it
+		case string:
+			args[i] = template.HTMLEscapeString(v)
+		case fmt.Stringer:
+			args[i] = template.HTMLEscapeString(v.String())
+		default:
+			args[i] = template.HTMLEscapeString(fmt.Sprint(v))
+		}
+	}
+	return template.HTML(fmt.Sprintf(s, args...))
+}