Move scoring in ES|QL out of snapshot

Author: tteofili

docs/reference/esql/metadata-fields.asciidoc

@@ -20,6 +20,8 @@ supported ones are:
   * <<mapping-ignored-field,`_ignored`>>: the ignored source document fields. The field is of the type
   <<keyword,keyword>>.
 
+  * `_score`: when enabled, the final score assigned to each row matching an ES|QL query.
+
 To enable the access to these fields, the <<esql-from,`FROM`>> source command needs
 to be provided with a dedicated directive:
 

x-pack/plugin/esql/src/main/antlr/EsqlBaseLexer.tokens

@@ -703,7 +703,7 @@ public enum Cap {
         /**
          * Support the "METADATA _score" directive to enable _score column.
          */
-        METADATA_SCORE(Build.current().isSnapshot()),
+        METADATA_SCORE,
 
         /**
          * Term function

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

@@ -262,8 +262,7 @@ public LogicalPlan visitFromCommand(EsqlBaseParser.FromCommandContext ctx) {
             for (var c : ctx.metadata().UNQUOTED_SOURCE()) {
                 String id = c.getText();
                 Source src = source(c);
-                if (MetadataAttribute.isSupported(id) == false // TODO: drop check below once METADATA_SCORE is no longer snapshot-only
-                    || (EsqlCapabilities.Cap.METADATA_SCORE.isEnabled() == false && MetadataAttribute.SCORE.equals(id))) {
+                if (MetadataAttribute.isSupported(id) == false) {
                     throw new ParsingException(src, "unsupported metadata field [" + id + "]");
                 }
                 Attribute a = metadataMap.put(id, MetadataAttribute.create(src, id));