Direct SVG rendering (#12157)

Introduce 'make svg' which calls a node script that compiles svg files
to `public/img/svg`. These files are vendored to not create a dependency
on Node for the backend build.

On the frontend side, configure webpack using `raw-loader` so SVGs can
be imported as string.

Also moved our existing SVGs to web_src/svg for consistency.

Fixes: https://github.com/go-gitea/gitea/issues/11618

modules/svg/svg.go

@@ -0,0 +1,13 @@
+// Copyright 2020 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 svg
+
+// SVGs contains discovered SVGs
+var SVGs map[string]string
+
+// Init discovers SVGs and populates the `SVGs` variable
+func Init() {
+	SVGs = Discover()
+}