Add object type (#1948)

Add a new type: Object. Currently, it's mainly for complex aggregate metrics(HLL , Bitmap).

The Object type has the following constraints：
1 Object type could not as key column type
2 Object type doesn't support all indices (BloomFilter, short key, zone map, invert index)
3 Object type doesn't support filter and group by

In the implementation：

The Object type reuse the StringValue and StringVal, because in storage engine, the Object type is binary, it has a pointer and length.

be/src/exprs/expr_context.cpp

@@ -335,10 +335,11 @@ void* ExprContext::get_value(Expr* e, TupleRow* row) {
     }
     case TYPE_CHAR:
     case TYPE_VARCHAR:
-    case TYPE_HLL: {
+    case TYPE_HLL:
+    case TYPE_OBJECT: {
         doris_udf::StringVal v = e->get_string_val(this, row);
         if (v.is_null) {
-            return NULL;
+            return nullptr;
         }
         _result.string_val.ptr = reinterpret_cast<char*>(v.ptr);
         _result.string_val.len = v.len;