YT-19324: move YT provider to ydb/library/yql

This commit is formed by the following script: https://paste.yandex-team.ru/6f92e4b8-efc5-4d34-948b-15ee2accd7e7/text.
This commit has zero effect on all projects that depend on YQL.

The summary of changes:
- `yql/providers/yt -> ydb/library/yql/providers/yt `- the whole implementation of YT provider is moved into YDB code base for further export as a part of YT YQL plugin shared library;
- `yql/providers/stat/{expr_nodes,uploader} -> ydb/library/yql/providers/stat/{expr_nodes,uploader}` - a small interface without implementation and the description of stat expr nodes;
- `yql/core/extract_predicate/ut -> ydb/library/yql/core/extract_predicate/ut`;
- `yql/core/{ut,ut_common} -> ydb/library/yql/core/{ut,ut_common}`;
- `yql/core` is gone;
- `yql/library/url_preprocessing -> ydb/library/yql/core/url_preprocessing`.

**NB**: all new targets inside `ydb/` are under `IF (NOT CMAKE_EXPORT)` clause which disables them from open-source cmake generation and ya make build. They will be enabled in the subsequent commits.

1 files changed, 39 insertions, 0 deletions

diff --git a/library/cpp/skiff/skiff_validator.h b/library/cpp/skiff/skiff_validator.h
new file mode 100644
index 0000000000..522cc74db6
--- /dev/null
+++ b/library/cpp/skiff/skiff_validator.h
@@ -0,0 +1,39 @@
+#pragma once
+
+#include "public.h"
+
+#include "skiff_schema.h"
+
+#include <util/string/cast.h>
+
+namespace NSkiff {
+
+////////////////////////////////////////////////////////////////////////////////
+
+class TValidatorNodeStack;
+
+////////////////////////////////////////////////////////////////////////////////
+
+class TSkiffValidator
+{
+public:
+    explicit TSkiffValidator(std::shared_ptr<TSkiffSchema> skiffSchema);
+    ~TSkiffValidator();
+
+    void BeforeVariant8Tag();
+    void OnVariant8Tag(ui8 tag);
+
+    void BeforeVariant16Tag();
+    void OnVariant16Tag(ui16 tag);
+
+    void OnSimpleType(EWireType value);
+
+    void ValidateFinished();
+
+private:
+    const std::unique_ptr<TValidatorNodeStack> Context_;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+
+} // namespace NSkiff