MNT Update URL unicode-org.github.io/icu (#10176)

A further addition to #10118

docs/en/02_Developer_Guides/03_Forms/Field_types/02_DateField.md

@@ -55,7 +55,7 @@ DateField::create('MyDate')
 ```
 
 [info]
-The formats are based on [ICU format](http://www.icu-project.org/apiref/icu4c/classSimpleDateFormat.html#details).
+The formats are based on [ICU format](https://unicode-org.github.io/icu/userguide/format_parse/datetime/#simpledateformat).
 [/info]
 
 

docs/en/02_Developer_Guides/13_i18n/index.md

@@ -94,7 +94,7 @@ i18n::config()
 
 Localization in Silverstripe CMS uses PHP's [intl extension](http://php.net/intl).
 Formats for it's [IntlDateFormatter](http://php.net/manual/en/class.intldateformatter.php)
-are defined in [ICU format](http://www.icu-project.org/apiref/icu4c/classSimpleDateFormat.html#details),
+are defined in [ICU format](https://unicode-org.github.io/icu/userguide/format_parse/datetime/#simpledateformat),
 not PHP's built-in [date()](http://nz.php.net/manual/en/function.date.php).
 
 These settings are not used for CMS presentation.

docs/en/04_Changelogs/4.0.0.md

@@ -1812,7 +1812,7 @@ usercode before invocation.
 * Moved `SapphireTest::resetDBSchema()` to `TempDatabase->resetSchema()`
 * `DBDate`, `DBTime` and `DBDatetime` have changed methods:
     * Added `getTimestamp()` to get the respective date / time as unix timestamp (seconds since 1970-01-01)
-    * Changed `Format()` method to use [CLDR format strings](http://userguide.icu-project.org/formatparse/datetime),
+    * Changed `Format()` method to use [CLDR format strings](https://unicode-org.github.io/icu/userguide/format_parse/datetime/),
       rather than [PHP format string](http://php.net/manual/en/function.date.php).
       E.g. `d/m/Y H:i:s` (php format) should be replaced with to `dd/MM/y HH:mm:ss` (CLDR format).
     * Added `getISOFormat()` to return the standard date/time ISO 8601 pattern in CLDR format.