Add initial version of scoring test

Author: svilen-mihaylov-elastic

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

@@ -114,6 +114,20 @@ book_no:keyword | title:text
 6151            | Pop! Went Another Balloon: A Magical Counting Storybook (Magical Counting Storybooks) | [Keith Faulkner, Rory Tyger]      | 5.975414276123047 
 ;
 
+testMultiMatchWithScore
+required_capability: multi_match_function
+required_capability: metadata_score
+
+from books metadata _score
+| where multi_match("Mark", "author", "title", {"fuzziness": 1})
+| keep book_no, title, author, _score;
+ignoreOrder:true
+
+book_no:keyword | title:text                                                                            | author:text                       | _score:double
+3535            | Rainbow's End: A Magical Story and Moneybox                                           | [Beverlie Manson, Keith Faulkner] | 6.5579609870910645
+6151            | Pop! Went Another Balloon: A Magical Counting Storybook (Magical Counting Storybooks) | [Keith Faulkner, Rory Tyger]      | 5.975414276123047 
+;
+
 multipleWhereWithMatchScoringNoSort
 required_capability: metadata_score
 required_capability: match_operator_colon

x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/plugin/ScoringIT.java

@@ -46,6 +46,7 @@ protected Collection<Class<? extends Plugin>> nodePlugins() {
     public static List<Object[]> params() {
         List<Object[]> params = new ArrayList<>();
         params.add(new Object[] { "match(content, \"fox\")" });
+        params.add(new Object[] { "multi_match(\"fox\", \"content\", {\"operator\": \"AND\"})" });
         params.add(new Object[] { "content:\"fox\"" });
         params.add(new Object[] { "qstr(\"content: fox\")" });
         params.add(new Object[] { "kql(\"content*: fox\")" });

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/fulltext/MultiMatch.java

@@ -311,7 +311,7 @@ private TypeResolution resolveFields() {
                 )
             )
             .reduce(TypeResolution::and)
-            .get();
+            .orElse(null);
     }
 
     private TypeResolution resolveOptions() {