Prettify number of issues (#17760)

* Prettify number of issues

- Use the PrettyNumber function to add commas in large amount of issues.

* Use client-side formatting

* prettify on both server and client

* remove unused i18n entries

* handle more cases, support other int types in PrettyNumber

* specify locale to avoid issues with node default locale

* remove superfluos argument

* introduce template helper, octicon tweaks, js refactor

* Update modules/templates/helper.go

* Apply some suggestions.

* Add comment

* Update templates/user/dashboard/issues.tmpl

Co-authored-by: silverwind <me@silverwind.io>

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

options/locale/locale_en-US.ini

@@ -1259,8 +1259,6 @@ issues.change_ref_at = `changed reference from <b><strike>%s</strike></b> to <b>
 issues.remove_ref_at = `removed reference <b>%s</b> %s`
 issues.add_ref_at = `added reference <b>%s</b> %s`
 issues.delete_branch_at = `deleted branch <b>%s</b> %s`
-issues.open_tab = %d Open
-issues.close_tab = %d Closed
 issues.filter_label = Label
 issues.filter_label_exclude = `Use <code>alt</code> + <code>click/enter</code> to exclude labels`
 issues.filter_label_no_select = All labels
@@ -1613,8 +1611,6 @@ pulls.auto_merge_newly_scheduled_comment = `scheduled this pull request to auto
 pulls.auto_merge_canceled_schedule_comment = `canceled auto merging this pull request when all checks succeed %[1]s`
 
 milestones.new = New Milestone
-milestones.open_tab = %d Open
-milestones.close_tab = %d Closed
 milestones.closed = Closed %s
 milestones.update_ago = Updated %s ago
 milestones.no_due_date = No due date