Allow using localized absolute date times within phrases with place holders and localize issue due date events (#24275)

This refactors the `shared/datetime/short|long|full` templates into a
template helper function, which allows us to render absolute date times
within translatable phrases.

- Follows #23988
- The first attempt was in #24055
- This should help #22664 

Changes:
1. Added the `DateTime` template helper that replaces the
`shared/datetime/short|long|full` templates
2. Used find-and-replace with varying regexes to replace the templates
from step 1 (for example, `\{\{template "shared/datetime/(\S+) \(dict
"Datetime" ([^"]+) "Fallback" ([^\)]+\)?) ?\)?\}\}` -> `{{DateTime "$1
$2 $3}}`)
3. Used the new `DateTime` helper in the issue due date timestamp
rendering

# Before

![image](https://user-images.githubusercontent.com/20454870/233791256-b454c455-aca0-4b76-b300-7866c7bd529e.png)

# After

![image](https://user-images.githubusercontent.com/20454870/233790809-c4913355-2822-4657-bb29-2298deb6d4b3.png)

---------

Signed-off-by: Yarden Shoham <git@yardenshoham.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

templates/repo/activity.tmpl

@@ -2,7 +2,7 @@
 <div role="main" aria-label="{{.Title}}" class="page-content repository commits">
 	{{template "repo/header" .}}
 	<div class="ui container">
-		<h2 class="ui header">{{template "shared/datetime/long" (dict "Datetime" .DateFrom "Fallback" .DateFrom)}} - {{template "shared/datetime/long" (dict "Datetime" .DateUntil "Fallback" .DateUntil)}}
+		<h2 class="ui header">{{DateTime "long" .DateFrom .DateFrom}} - {{DateTime "long" .DateUntil .DateUntil}}
 			<div class="ui right">
 				<!-- Period -->
 				<div class="ui floating dropdown jump filter">