Respect user's locale when rendering the date range in the repo activity page (#21410)

# Description
Previously, to make the date range understood by all, we used the format
"2006-01-02" for the dates as it's locale-generic.

This commit changes the rendering logic. Instead of rendering the date
on the server, we send a formatted computer-readable timestamp. The
client's javascript then renders it according to the user's locale.

This approach is reusable across the codebase, any `<time></time>` tag
with the data-format="date" attribute would get rendered according to
the user's chosen locale.

## Previous View

![image](https://user-images.githubusercontent.com/20454870/195099143-e1c5df86-282a-42f1-898f-a36bb5fe7c2f.png)

## New View

### English

![image](https://user-images.githubusercontent.com/20454870/195099301-5cda4eab-4012-49d5-97e5-b1f9cada9c06.png)

### French

![image](https://user-images.githubusercontent.com/20454870/195099434-ce23e394-8d65-4c4c-8ac8-8b96bc9044f3.png)

### Portuguese

![image](https://user-images.githubusercontent.com/20454870/195099559-9a7aed28-944a-45ec-bedb-64403e3faede.png)

### Italian

![image](https://user-images.githubusercontent.com/20454870/195099661-17758d55-3fe0-4797-879b-d45de0ee8ba3.png)

# References
* #21380 
* #21387
* #21396

Inspiration:

I think either differentiating by class, or probably better by a custom
attribute such as `data-format` or similar, is the best course of
action.

_Originally posted by @delvh in
https://github.com/go-gitea/gitea/issues/21396#issuecomment-1274424788_
      


Resolves #21380

Signed-off-by: Yarden Shoham <hrsi88@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>

routers/web/repo/activity.go

@@ -47,8 +47,8 @@ func Activity(ctx *context.Context) {
 		ctx.Data["Period"] = "weekly"
 		timeFrom = timeUntil.Add(-time.Hour * 168)
 	}
-	ctx.Data["DateFrom"] = timeFrom.Format("2006-01-02")
+	ctx.Data["DateFrom"] = timeFrom.UTC().Format(time.RFC3339)
-	ctx.Data["DateUntil"] = timeUntil.Format("2006-01-02")
+	ctx.Data["DateUntil"] = timeUntil.UTC().Format(time.RFC3339)
 	ctx.Data["PeriodText"] = ctx.Tr("repo.activity.period." + ctx.Data["Period"].(string))
 
 	var err error

templates/repo/activity.tmpl

@@ -2,7 +2,7 @@
 <div class="page-content repository commits">
 	{{template "repo/header" .}}
 	<div class="ui container">
-		<h2 class="ui header">{{.DateFrom}} - {{.DateUntil}}
+		<h2 class="ui header"><time data-format="date" datetime="{{.DateFrom}}">{{.DateFrom}}</time> - <time data-format="date" datetime="{{.DateUntil}}">{{.DateUntil}}</time>
 			<div class="ui right">
 				<!-- Period -->
 				<div class="ui floating dropdown jump filter">

web_src/js/features/formatting.js

@@ -1,6 +1,7 @@
 import {prettyNumber} from '../utils.js';
 
 const {lang} = document.documentElement;
+const dateFormatter = new Intl.DateTimeFormat(lang, {year: 'numeric', month: 'long', day: 'numeric'});
 
 export function initFormattingReplacements() {
   // replace english formatted numbers with locale-specific separators
@@ -11,4 +12,10 @@ export function initFormattingReplacements() {
       el.textContent = formatted;
     }
   }
+
+  // for each <time></time> tag, if it has the data-format="date" attribute, format
+  // the text according to the user's chosen locale
+  for (const timeElement of document.querySelectorAll('time[data-format="date"]')) {
+    timeElement.textContent = dateFormatter.format(new Date(timeElement.dateTime));
+  }
 }