GH-48560: [C++][Parquet] When fuzzing, treat Table validation error as hard error (#48863)

### Rationale for this change

Currently, when fuzzing a Parquet file, proper errors are ignored since the file is most of the time simply invalid: it's ok to get an error.

However, if reading a Parquet row group was successful, the Parquet reader should have ensured that the resulting Table is structurally sound: calling `Table::Validate` should succeed, and if it fails then it should report a bug.

### What changes are included in this PR?

Call `Table::Validate` on a successful read from the Parquet fuzz target, and abort if validation fails.

`Table::ValidateFull`, however, is allowed to fail, as for example a Parquet UTF8 column could contain invalid UTF8 bytes, and we don't detect that when decoding.

### Are these changes tested?

By existing tests and fuzz regression files.

Actual running this on OSS-Fuzz will tell us if this is really a good idea.

### Are there any user-facing changes?

No.

* GitHub Issue: #48560

Authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Antoine Pitrou <antoine@python.org>

Author: pitrou

cpp/src/parquet/arrow/fuzz_internal.cc

@@ -26,6 +26,7 @@
 #include "arrow/table.h"
 #include "arrow/util/base64.h"
 #include "arrow/util/fuzz_internal.h"
+#include "arrow/util/logging.h"
 #include "arrow/util/string.h"
 #include "parquet/arrow/reader.h"
 #include "parquet/bloom_filter.h"
@@ -95,16 +96,20 @@ std::shared_ptr<DecryptionKeyRetriever> MakeKeyRetriever() {
 namespace {
 
 Status FuzzReadData(std::unique_ptr<FileReader> reader) {
-  auto st = Status::OK();
+  auto final_status = Status::OK();
   for (int i = 0; i < reader->num_row_groups(); ++i) {
     std::shared_ptr<Table> table;
     auto row_group_status = reader->ReadRowGroup(i, &table);
     if (row_group_status.ok()) {
+      // When reading returns successfully, the Arrow data should be structurally
+      // valid so that it can be read normally. If that is not the case, abort
+      // so that the error can be published by OSS-Fuzz.
+      ARROW_CHECK_OK(table->Validate());
       row_group_status &= table->ValidateFull();
     }
-    st &= row_group_status;
+    final_status &= row_group_status;
   }
-  return st;
+  return final_status;
 }
 
 template <typename DType>