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>

modules/templates/helper.go

@@ -139,6 +139,7 @@ func NewFuncMap() []template.FuncMap {
 		"CountFmt":      base.FormatNumberSI,
 		"TimeSince":     timeutil.TimeSince,
 		"TimeSinceUnix": timeutil.TimeSinceUnix,
+		"DateTime":      timeutil.DateTime,
 		"Sec2Time":      util.SecToTime,
 		"DateFmtLong": func(t time.Time) string {
 			return t.Format(time.RFC3339)