New capability for ::date casting

Author: kanoshiou

x-pack/plugin/esql/qa/testFixtures/src/main/resources/convert.csv-spec

@@ -75,7 +75,7 @@ ROW date="1985-01-01T00:00:00Z"::datetime, zero=0::datetime
 ;
 
 convertToDate
-required_capability: casting_operator
+required_capability: casting_operator_for_date
 ROW date="1985-01-01T00:00:00Z"::date, zero=0::date
 ;
 

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/action/EsqlCapabilities.java

@@ -112,6 +112,11 @@ public enum Cap {
          */
         CASTING_OPERATOR,
 
+        /**
+         * Support for the ::date casting operator
+         */
+        CASTING_OPERATOR_FOR_DATE,
+
         /**
          * Blocks can be labelled with {@link org.elasticsearch.compute.data.Block.MvOrdering#SORTED_ASCENDING} for optimizations.
          */