Drop fomantic build (#33845)

We would never update or build fomantic again, we have forked it as a
private library long time ago.

So just put the JS and CSS files in "fomantic/build" into git. And use
"import" to use them.

Remove "form.js", rewrite "tab" component.

All source code is from official Fomantic UI build. Will apply patches
in separate PRs.

.gitattributes

@@ -5,7 +5,5 @@
 /public/assets/img/svg/*.svg linguist-generated
 /templates/swagger/v1_json.tmpl linguist-generated
 /vendor/** -text -eol linguist-vendored
-/web_src/fomantic/build/** linguist-generated
-/web_src/fomantic/_site/globals/site.variables linguist-language=Less
 /web_src/js/vendor/** -text -eol linguist-vendored
 Dockerfile.* linguist-language=Dockerfile