Add test locale

Add en-UK locale with same short count as en-US.

packages/core/src/systems/en-UK/index.ts

@@ -0,0 +1 @@
+export * as shortCount from '../en-US/short-count';

packages/core/src/systems/index.ts

@@ -1 +1,2 @@
 export * as enUS from './en-US';
+export * as enUK from './en-UK';

packages/example-web/index.html

@@ -104,6 +104,9 @@
 						<option value="enUS">
 							English (US)
 						</option>
+						<option value="enUK">
+							English (UK)
+						</option>
 					</select>
 					<select class="select" aria-label="Variant" name="system.count">
 						<option value="shortCount">