Introduce GiteaLocaleNumber custom element to handle number localization on pages. (#23861)

Follow #21429 & #22861

Use `<gitea-locale-number>` instead of backend `PrettyNumber`. All old
`PrettyNumber` related functions are removed. A lot of code could be
simplified.

And some functions haven't been used for long time (dead code), so they
are also removed by the way (eg: `SplitStringAtRuneN`, `Dedent`)

This PR only tries to improve the `PrettyNumber` rendering problem, it
doesn't touch the "plural" problem.

Screenshot:


![image](https://user-images.githubusercontent.com/2114189/229290804-1f63db65-1e34-4a54-84ba-e00b44331b17.png)


![image](https://user-images.githubusercontent.com/2114189/229290911-c88dea00-b11d-48dd-accb-9f52edd73ce4.png)

modules/base/tool.go

@@ -22,7 +22,6 @@ import (
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
-	"code.gitea.io/gitea/modules/util"
 
 	"github.com/dustin/go-humanize"
 	"github.com/minio/sha256-simd"
@@ -142,12 +141,6 @@ func FileSize(s int64) string {
 	return humanize.IBytes(uint64(s))
 }
 
-// PrettyNumber produces a string form of the given number in base 10 with
-// commas after every three orders of magnitude
-func PrettyNumber(i interface{}) string {
-	return humanize.Comma(util.NumberIntoInt64(i))
-}
-
 // Subtract deals with subtraction of all types of number.
 func Subtract(left, right interface{}) interface{} {
 	var rleft, rright int64