Use auto-updating, natively hoverable, localized time elements (#23988)

- Added [GitHub's `relative-time` element](https://github.com/github/relative-time-element)
- Converted all formatted timestamps to use this element
- No more flashes of unstyled content around time elements
- These elements are localized using the `lang` property of the HTML file
- Relative (e.g. the activities in the dashboard) and duration (e.g.
server uptime in the admin page) time elements are auto-updated to keep
up with the current time without refreshing the page
- Code that is not needed anymore such as `formatting.js` and parts of `since.go` have been deleted

Replaces #21440
Follows #22861

## Screenshots

### Localized

![image](https://user-images.githubusercontent.com/20454870/230775041-f0af4fda-8f6b-46d3-b8e3-d340c791a50c.png)

![image](https://user-images.githubusercontent.com/20454870/230673393-931415a9-5729-4ac3-9a89-c0fb5fbeeeb7.png)

### Tooltips

#### Native for dates

![image](https://user-images.githubusercontent.com/20454870/230797525-1fa0a854-83e3-484c-9da5-9425ab6528a3.png)

#### Interactive for relative

![image](https://user-images.githubusercontent.com/115237/230796860-51e1d640-c820-4a34-ba2e-39087020626a.png)

### Auto-update

![rec](https://user-images.githubusercontent.com/20454870/230672159-37480d8f-435a-43e9-a2b0-44073351c805.gif)

---------

Signed-off-by: Yarden Shoham <git@yardenshoham.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: delvh <dev.lh@web.de>

modules/timeutil/since_test.go

@@ -5,7 +5,6 @@ package timeutil
 
 import (
 	"context"
-	"fmt"
 	"os"
 	"testing"
 	"time"
@@ -40,46 +39,6 @@ func TestMain(m *testing.M) {
 	os.Exit(retVal)
 }
 
-func TestTimeSince(t *testing.T) {
-	assert.Equal(t, "now", timeSince(BaseDate, BaseDate, translation.NewLocale("en-US")))
-
-	// test that each diff in `diffs` yields the expected string
-	test := func(expected string, diffs ...time.Duration) {
-		t.Run(expected, func(t *testing.T) {
-			for _, diff := range diffs {
-				actual := timeSince(BaseDate, BaseDate.Add(diff), translation.NewLocale("en-US"))
-				assert.Equal(t, translation.NewLocale("en-US").Tr("tool.ago", expected), actual)
-				actual = timeSince(BaseDate.Add(diff), BaseDate, translation.NewLocale("en-US"))
-				assert.Equal(t, translation.NewLocale("en-US").Tr("tool.from_now", expected), actual)
-			}
-		})
-	}
-	test("1 second", time.Second, time.Second+50*time.Millisecond)
-	test("2 seconds", 2*time.Second, 2*time.Second+50*time.Millisecond)
-	test("1 minute", time.Minute, time.Minute+29*time.Second)
-	test("2 minutes", 2*time.Minute, time.Minute+30*time.Second)
-	test("2 minutes", 2*time.Minute, 2*time.Minute+29*time.Second)
-	test("1 hour", time.Hour, time.Hour+29*time.Minute)
-	test("2 hours", 2*time.Hour, time.Hour+30*time.Minute)
-	test("2 hours", 2*time.Hour, 2*time.Hour+29*time.Minute)
-	test("3 hours", 3*time.Hour, 2*time.Hour+30*time.Minute)
-	test("1 day", DayDur, DayDur+11*time.Hour)
-	test("2 days", 2*DayDur, DayDur+12*time.Hour)
-	test("2 days", 2*DayDur, 2*DayDur+11*time.Hour)
-	test("3 days", 3*DayDur, 2*DayDur+12*time.Hour)
-	test("1 week", WeekDur, WeekDur+3*DayDur)
-	test("2 weeks", 2*WeekDur, WeekDur+4*DayDur)
-	test("2 weeks", 2*WeekDur, 2*WeekDur+3*DayDur)
-	test("3 weeks", 3*WeekDur, 2*WeekDur+4*DayDur)
-	test("1 month", MonthDur, MonthDur+14*DayDur)
-	test("2 months", 2*MonthDur, MonthDur+15*DayDur)
-	test("2 months", 2*MonthDur, 2*MonthDur+14*DayDur)
-	test("1 year", YearDur, YearDur+5*MonthDur)
-	test("2 years", 2*YearDur, YearDur+6*MonthDur)
-	test("2 years", 2*YearDur, 2*YearDur+5*MonthDur)
-	test("3 years", 3*YearDur, 2*YearDur+6*MonthDur)
-}
-
 func TestTimeSincePro(t *testing.T) {
 	assert.Equal(t, "now", timeSincePro(BaseDate, BaseDate, translation.NewLocale("en-US")))
 
@@ -113,60 +72,6 @@ func TestTimeSincePro(t *testing.T) {
 			12*time.Minute+17*time.Second)
 }
 
-func TestHtmlTimeSince(t *testing.T) {
-	setting.TimeFormat = time.UnixDate
-	setting.DefaultUILocation = time.UTC
-	// test that `diff` yields a result containing `expected`
-	test := func(expected string, diff time.Duration) {
-		actual := htmlTimeSince(BaseDate, BaseDate.Add(diff), translation.NewLocale("en-US"))
-		assert.Contains(t, actual, `data-tooltip-content="Sat Jan  1 00:00:00 UTC 2000"`)
-		assert.Contains(t, actual, expected)
-	}
-	test("1 second", time.Second)
-	test("3 minutes", 3*time.Minute+5*time.Second)
-	test("1 day", DayDur+11*time.Hour)
-	test("1 week", WeekDur+3*DayDur)
-	test("3 months", 3*MonthDur+2*WeekDur)
-	test("2 years", 2*YearDur)
-	test("3 years", 2*YearDur+11*MonthDur+4*WeekDur)
-}
-
-func TestComputeTimeDiff(t *testing.T) {
-	// test that for each offset in offsets,
-	// computeTimeDiff(base + offset) == (offset, str)
-	test := func(base int64, str string, offsets ...int64) {
-		for _, offset := range offsets {
-			t.Run(fmt.Sprintf("%s:%d", str, offset), func(t *testing.T) {
-				diff, diffStr := computeTimeDiff(base+offset, translation.NewLocale("en-US"))
-				assert.Equal(t, offset, diff)
-				assert.Equal(t, str, diffStr)
-			})
-		}
-	}
-	test(0, "now", 0)
-	test(1, "1 second", 0)
-	test(2, "2 seconds", 0)
-	test(Minute, "1 minute", 0, 1, 29)
-	test(Minute, "2 minutes", 30, Minute-1)
-	test(2*Minute, "2 minutes", 0, 29)
-	test(2*Minute, "3 minutes", 30, Minute-1)
-	test(Hour, "1 hour", 0, 1, 29*Minute)
-	test(Hour, "2 hours", 30*Minute, Hour-1)
-	test(5*Hour, "5 hours", 0, 29*Minute)
-	test(Day, "1 day", 0, 1, 11*Hour)
-	test(Day, "2 days", 12*Hour, Day-1)
-	test(5*Day, "5 days", 0, 11*Hour)
-	test(Week, "1 week", 0, 1, 3*Day)
-	test(Week, "2 weeks", 4*Day, Week-1)
-	test(3*Week, "3 weeks", 0, 3*Day)
-	test(Month, "1 month", 0, 1)
-	test(Month, "2 months", 16*Day, Month-1)
-	test(10*Month, "10 months", 0, 13*Day)
-	test(Year, "1 year", 0, 179*Day)
-	test(Year, "2 years", 180*Day, Year-1)
-	test(3*Year, "3 years", 0, 179*Day)
-}
-
 func TestMinutesToFriendly(t *testing.T) {
 	// test that a number of minutes yields the expected string
 	test := func(expected string, minutes int) {