Move svg html render to modules/svg (#21716)

Also added more checks for the render function.

Co-authored-by: silverwind <me@silverwind.io>

modules/html/html.go

@@ -0,0 +1,34 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package html
+
+// 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 ...interface{}) (int, string) {
+	if len(others) == 0 {
+		return defaultSize, defaultClass
+	}
+
+	size := defaultSize
+	_size, ok := others[0].(int)
+	if ok && _size != 0 {
+		size = _size
+	}
+
+	if len(others) == 1 {
+		return size, defaultClass
+	}
+
+	class := defaultClass
+	if _class, ok := others[1].(string); ok && _class != "" {
+		if defaultClass == "" {
+			class = _class
+		} else {
+			class = defaultClass + " " + _class
+		}
+	}
+
+	return size, class
+}