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-no-newline.svg

@@ -0,0 +1 @@
+<svg viewBox="0 0 16 16" class="svg octicon-no-newline" width="16" height="16" aria-hidden="true"><path fill-rule="evenodd" d="M16 5v3c0 .55-.45 1-1 1h-3v2L9 8l3-3v2h2V5h2zM8 8c0 2.2-1.8 4-4 4s-4-1.8-4-4 1.8-4 4-4 4 1.8 4 4zM1.5 9.66L5.66 5.5C5.18 5.19 4.61 5 4 5 2.34 5 1 6.34 1 8c0 .61.19 1.17.5 1.66zM7 8c0-.61-.19-1.17-.5-1.66L2.34 10.5c.48.31 1.05.5 1.66.5 1.66 0 3-1.34 3-3z"/></svg>