Make GenericDialect support trailing commas in projections

Similar to apache#1911.

The docs for GenericDialect says that is can be permissive, so I thought
it could support trailing commas in projections.

This would help a bit on the "friendly sql" issue
apache/datafusion#14514

Author: simonvandel

src/dialect/generic.rs

@@ -116,6 +116,10 @@ impl Dialect for GenericDialect {
         true
     }
 
+    fn supports_projection_trailing_commas(&self) -> bool {
+        true
+    }
+
     fn supports_asc_desc_in_column_definition(&self) -> bool {
         true
     }