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/features/captcha.css

@@ -0,0 +1,33 @@
+.m-captcha-style {
+  width: 100%;
+  height: 5em;
+  vertical-align: middle;
+  display: inline-block;
+}
+
+@media (min-width: 768px) {
+  .g-recaptcha-style,
+  .h-captcha-style {
+    margin: 0 auto !important;
+    width: 304px;
+    padding-left: 30px;
+  }
+  .g-recaptcha-style iframe,
+  .h-captcha-style iframe {
+    border-radius: var(--border-radius) !important;
+    width: 302px !important;
+    height: 76px !important;
+  }
+  .m-captcha-style {
+    max-width: 450px;
+  }
+}
+
+@media (max-height: 575px) {
+  #rc-imageselect, /* google recaptcha */
+  .g-recaptcha-style,
+  .h-captcha-style {
+    transform: scale(0.77);
+    transform-origin: 0 0;
+  }
+}