Refactor locale number (#24134)

Before, the `GiteaLocaleNumber.js` was just written as a a drop-in
replacement for old `js-pretty-number`.

Actually, we can use Golang's `text` package to format.

This PR partially completes the TODOs in `GiteaLocaleNumber.js`:

> if we have complete backend locale support (eg: Golang "x/text"
package), we can drop this component.
> tooltip: only 2 usages of this, we can replace it with Golang's
"x/text/number" package in the future.

This PR also helps #24131

Screenshots:

<details>

![image](https://user-images.githubusercontent.com/2114189/232179420-b1b9974b-9d96-4408-b209-b80182c8b359.png)


![image](https://user-images.githubusercontent.com/2114189/232179416-14f36aa0-3f3e-4ac9-b366-7bd3a4464a11.png)

</details>

modules/translation/mock.go

@@ -0,0 +1,27 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package translation
+
+import "fmt"
+
+// MockLocale provides a mocked locale without any translations
+type MockLocale struct{}
+
+var _ Locale = (*MockLocale)(nil)
+
+func (l MockLocale) Language() string {
+	return "en"
+}
+
+func (l MockLocale) Tr(s string, _ ...interface{}) string {
+	return s
+}
+
+func (l MockLocale) TrN(_cnt interface{}, key1, _keyN string, _args ...interface{}) string {
+	return key1
+}
+
+func (l MockLocale) PrettyNumber(v any) string {
+	return fmt.Sprint(v)
+}