chore: use default schema from Dialect (googleapis#1745)

Author: olavloite

src/main/java/com/google/cloud/spanner/jdbc/JdbcConnection.java

@@ -523,14 +523,7 @@ public String getSchema() throws SQLException {
 
   @Nonnull
   String getDefaultSchema() {
-    // TODO: Update to use getDialect()#getDefaultSchema() when available.
-    switch (getDialect()) {
-      case POSTGRESQL:
-        return "public";
-      case GOOGLE_STANDARD_SQL:
-      default:
-        return "";
-    }
+    return getDialect().getDefaultSchema();
   }
 
   @Override

src/test/java/com/google/cloud/spanner/jdbc/JdbcConnectionTest.java

@@ -738,6 +738,8 @@ public void testSchema() throws SQLException {
       // The default schema is the empty string for GoogleSQL databases.
       // The default schema is 'public' for PostgreSQL databases.
       assertEquals(connection.getDefaultSchema(), connection.getSchema());
+      String expectedDefaultSchema = dialect == Dialect.POSTGRESQL ? "public" : "";
+      assertEquals(expectedDefaultSchema, connection.getSchema());
       // This should be allowed.
       connection.setSchema(connection.getDefaultSchema());
       JdbcSqlExceptionImpl exception =