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

public/img/svg/octicon-request-changes.svg

@@ -0,0 +1 @@
+<svg viewBox="0 0 16 16" class="svg octicon-request-changes" width="16" height="16" aria-hidden="true"><path fill-rule="evenodd" d="M0 1a1 1 0 011-1h14a1 1 0 011 1v10a1 1 0 01-1 1H7.5L4 15.5V12H1a1 1 0 01-1-1V1zm1 0v10h4v2l2-2h8V1H1zm7.5 3h2v1h-2v2h-1V5h-2V4h2V2h1v2zm2 5h-5V8h5v1z"/></svg>