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, 16 insertions, 0 deletions

diff --git a/library/cpp/skiff/ya.make b/library/cpp/skiff/ya.make
new file mode 100644
index 0000000000..ff3eb55c9f
--- /dev/null
+++ b/library/cpp/skiff/ya.make
@@ -0,0 +1,16 @@
+LIBRARY()
+
+SRCS(
+  skiff.cpp
+  skiff_schema.cpp
+  skiff_validator.cpp
+  zerocopy_output_writer.cpp
+)
+
+GENERATE_ENUM_SERIALIZATION(public.h)
+
+END()
+
+RECURSE_FOR_TESTS(
+  unittests
+)