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/css/index.css

@@ -19,6 +19,7 @@
 @import "./modules/dimmer.css";
 @import "./modules/modal.css";
 @import "./modules/tab.css";
+@import "./modules/form.css";
 
 @import "./modules/tippy.css";
 @import "./modules/breadcrumb.css";
@@ -42,6 +43,7 @@
 @import "./features/expander.css";
 @import "./features/cropper.css";
 @import "./features/console.css";
+@import "./features/captcha.css";
 
 @import "./markup/content.css";
 @import "./markup/codecopy.css";
@@ -54,7 +56,6 @@
 @import "./base.css";
 @import "./home.css";
 @import "./install.css";
-@import "./form.css";
 
 @import "./repo.css";
 @import "./repo/release-tag.css";