Address review feedback for CREATE INDEX ASYNC

- Add DSQL docs link to the async field
- Simplify async index tests to round-trip verified_stmt calls
- Move async index tests from sqlparser_postgres.rs to sqlparser_common.rs

Author: amaksimo

src/ast/ddl.rs

@@ -2819,6 +2819,7 @@ pub struct CreateIndex {
     /// whether the index is created concurrently
     pub concurrently: bool,
     /// whether the index is created asynchronously
+    /// [DSQL]: <https://docs.aws.amazon.com/aurora-dsql/latest/userguide/working-with-create-index-async.html>
     pub r#async: bool,
     /// IF NOT EXISTS clause
     pub if_not_exists: bool,

tests/sqlparser_common.rs

@@ -9623,6 +9623,12 @@ fn test_create_index_with_with_clause() {
     }
 }
 
+#[test]
+fn parse_create_index_async() {
+    verified_stmt("CREATE INDEX ASYNC my_index ON my_table(col1)");
+    verified_stmt("CREATE UNIQUE INDEX ASYNC my_index ON my_table(col1)");
+}
+
 #[test]
 fn parse_drop_index() {
     let sql = "DROP INDEX idx_a";

tests/sqlparser_postgres.rs

@@ -3227,26 +3227,6 @@ fn parse_create_index_concurrently() {
     }
 }
 
-#[test]
-fn parse_create_index_async() {
-    pg().verified_stmt("CREATE INDEX ASYNC my_index ON my_table(col1)"); 
-
-    let sql = "CREATE UNIQUE INDEX ASYNC my_index ON my_table(col1)";
-    match pg().verified_stmt(sql) {
-        Statement::CreateIndex(CreateIndex {
-            unique,
-            concurrently,
-            r#async,
-            ..
-        }) => {
-            assert!(unique);
-            assert!(!concurrently);
-            assert!(r#async);
-        }
-        _ => unreachable!(),
-    }
-}
-
 #[test]
 fn parse_create_index_with_predicate() {
     let sql = "CREATE INDEX IF NOT EXISTS my_index ON my_table(col1, col2) WHERE col3 IS NULL";