Use auto-updating, natively hoverable, localized time elements (#23988)

- Added [GitHub's `relative-time` element](https://github.com/github/relative-time-element)
- Converted all formatted timestamps to use this element
- No more flashes of unstyled content around time elements
- These elements are localized using the `lang` property of the HTML file
- Relative (e.g. the activities in the dashboard) and duration (e.g.
server uptime in the admin page) time elements are auto-updated to keep
up with the current time without refreshing the page
- Code that is not needed anymore such as `formatting.js` and parts of `since.go` have been deleted

Replaces #21440
Follows #22861

## Screenshots

### Localized

![image](https://user-images.githubusercontent.com/20454870/230775041-f0af4fda-8f6b-46d3-b8e3-d340c791a50c.png)

![image](https://user-images.githubusercontent.com/20454870/230673393-931415a9-5729-4ac3-9a89-c0fb5fbeeeb7.png)

### Tooltips

#### Native for dates

![image](https://user-images.githubusercontent.com/20454870/230797525-1fa0a854-83e3-484c-9da5-9425ab6528a3.png)

#### Interactive for relative

![image](https://user-images.githubusercontent.com/115237/230796860-51e1d640-c820-4a34-ba2e-39087020626a.png)

### Auto-update

![rec](https://user-images.githubusercontent.com/20454870/230672159-37480d8f-435a-43e9-a2b0-44073351c805.gif)

---------

Signed-off-by: Yarden Shoham <git@yardenshoham.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: delvh <dev.lh@web.de>

web_src/js/webcomponents/README.md

@@ -10,9 +10,3 @@ https://developer.mozilla.org/en-US/docs/Web/Web_Components
   so they should have their own dependencies and should be very light,
   then they won't affect the page loading time too much.
 * If the component is not a public one, it's suggested to have its own `Gitea` or `gitea-` prefix to avoid conflicts.
-
-# TODO
-
-There are still some components that are not migrated to web components yet:
-
-* `<time data-format>`

web_src/js/webcomponents/webcomponents.js

@@ -1,3 +1,4 @@
 import '@webcomponents/custom-elements'; // polyfill for some browsers like Pale Moon
+import '@github/relative-time-element';
 import './GiteaLocaleNumber.js';
 import './GiteaOriginUrl.js';