Refactor locale number (#24134)

Before, the `GiteaLocaleNumber.js` was just written as a a drop-in
replacement for old `js-pretty-number`.

Actually, we can use Golang's `text` package to format.

This PR partially completes the TODOs in `GiteaLocaleNumber.js`:

> if we have complete backend locale support (eg: Golang "x/text"
package), we can drop this component.
> tooltip: only 2 usages of this, we can replace it with Golang's
"x/text/number" package in the future.

This PR also helps #24131

Screenshots:

<details>

![image](https://user-images.githubusercontent.com/2114189/232179420-b1b9974b-9d96-4408-b209-b80182c8b359.png)


![image](https://user-images.githubusercontent.com/2114189/232179416-14f36aa0-3f3e-4ac9-b366-7bd3a4464a11.png)

</details>

web_src/js/webcomponents/webcomponents.js

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