Add :date and :time functions (#570)

* Add :date and :time aliases

* Define as standalone functions instead

* Add hourCycle option to :time

* Drop non-style options, use XML time & date validation rules

Author: eemeli

spec/registry.xml

@@ -9,6 +9,10 @@
   <validationRule id="anything" regex=".*"/>
   <validationRule id="anythingNotEmpty" regex=".+"/>
   <validationRule id="iso8601" regex="\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}"/>
+  <validationRule id="xmlDate"
+    regex="-?([1-9][0-9]{3,}|0[0-9]{3})-(0[1-9]|1[0-2])-(0[1-9]|[12][0-9]|3[01])(Z|[+-]((0[0-9]|1[0-3]):[0-5][0-9]|14:00))?"/>
+  <validationRule id="xmlTime"
+    regex="(([01][0-9]|2[0-3])(:[0-5][0-9]){2}(\.[0-9]+)?|24:00:00(\.0+)?)(Z|[+-]((0[0-9]|1[0-3]):[0-5][0-9]|14:00))?"/>
 
   <function name="datetime">
     <!-- https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DateTimeFormat/DateTimeFormat -->
@@ -141,7 +145,36 @@
         </description>
       </option>
     </formatSignature>
+  </function>
+
+  <function name="date">
+    <description>
+      Date formatting
+    </description>
 
+    <formatSignature>
+      <input validationRule="xmlDate"/>
+      <option name="style" values="full long medium short">
+        <description>
+          The predefined date formatting style to use.
+        </description>
+      </option>
+    </formatSignature>
+  </function>
+
+  <function name="time">
+    <description>
+      Time formatting
+    </description>
+
+    <formatSignature>
+      <input validationRule="xmlTime"/>
+      <option name="style" values="full long medium short">
+        <description>
+          The predefined time formatting style to use.
+        </description>
+      </option>
+    </formatSignature>
   </function>
 
   <function name="number">