[fix](struct-type) fix struct subtype support (#17081)

1. Make sure all sub types which STRUCT supported work correctly;
2. remove unused variable `_need_validate_data`;
3. lazy init min or max decimal to support nested DecimalV2 column validate;

Co-authored-by: cambyzju <zhuxiaoli01@baidu.com>

fe/fe-core/src/main/java/org/apache/doris/analysis/StructLiteral.java

@@ -43,7 +43,7 @@ public class StructLiteral extends LiteralExpr {
         type = new StructType();
         children = new ArrayList<>();
         for (LiteralExpr expr : exprs) {
-            if (!type.supportSubType(expr.getType())) {
+            if (!expr.getType().isNull() && !type.supportSubType(expr.getType())) {
                 throw new AnalysisException("Invalid element type in STRUCT.");
             }
             ((StructType) type).addField(new StructField(expr.getType()));