Various code was using fomantic `loading` class which I think got broken
a while ago and rendered only a full circle. Fix those to use
`is-loading`.
Before:
<img width="295" alt="Screenshot 2024-03-19 at 22 56 26"
src="dbe83395-5db4-4868-90bc-3613866a35f0">
After:
<img width="60" alt="Screenshot 2024-03-19 at 22 54 35"
src="8ac19b7e-035a-4c6d-850b-53a234ef69c2">
<img width="294" alt="Screenshot 2024-03-19 at 22 54 56"
src="34e819d7-25f7-43a1-9d48-4a68dcd2b6ad">
<img width="320" alt="Screenshot 2024-03-19 at 22 55 16"
src="05127544-47ff-4e18-9fd8-c84e44c374f8">
<img width="153" alt="Screenshot 2024-03-19 at 23 01 43"
src="a33248c6-b11d-40ff-82d8-f5a3d85b55aa">
<img width="1300" alt="Screenshot 2024-03-19 at 23 56 25"
src="562ca876-b5d5-4295-961e-9d2cdab31ab0">
<img width="136" alt="Screenshot 2024-03-20 at 00 00 38"
src="44838ac4-67f3-4fec-a8e3-978cc5dbdb72">
(cherry picked from commit d6fed9ab88b13e124c5e59ceac5b21a3af52ad24)
The old code used complex `if` blocks and strange HTML layouts.
<details>
</details>
This PR refactors the template code and remove legacy CSS styles. The UI
doesn't change much.
Ran most of the Less files through the Less compiler and Prettier and
then followed up with a round of manual fixes.
The Less compiler had unfortunately stripped all `//` style comments
that I had to restore (It did preserve `/* */` comments). Other fixes
include duplicate selector removal which were revealed after the
transpilation and which weren't caught by stylelint before but now are.
Fixes: https://github.com/go-gitea/gitea/issues/15565
