Remove fomantic form module (#36222)

- Replace fomantic form CSS with custom module
- Moved code in `form.css` to `modules/form.css`, removed around 70% of
the previous module.
- Moved captcha styles previously in `form.css` to its own file.

There is probably more unused CSS, like form error state colors which to
my knowledge is not used anywhere, but I'm not sure about that one so I
kept it.

One notable change is the removal of `type` combinator here, which
lowers the selector specificity and I noticed one issue where selector
`.ui.search > .prompt` was winning, so I added a workaround for that
until the `search` module can be removed as well.

```css
.ui.form .fields.error .field input:not([type])
.ui.form .fields.error .field input[type="date"]
```

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

web_src/fomantic/build/fomantic.css

@@ -1,4 +1,3 @@
 @import "./components/dropdown.css";
-@import "./components/form.css";
 @import "./components/modal.css";
 @import "./components/search.css";

web_src/fomantic/semantic.json

@@ -23,7 +23,6 @@
   "components": [
     "api",
     "dropdown",
-    "form",
     "modal",
     "search",
     "tab"