YT-19210: expose YQL shared library for YT.

After this, a new target libyqlplugin.so appears. in open-source cmake build.
Diff in open-source YDB repo looks like the following: https://paste.yandex-team.ru/f302bdb4-7ef2-4362-91c7-6ca45f329264

1 files changed, 74 insertions, 0 deletions

diff --git a/yt/yql/plugin/bridge/interface.h b/yt/yql/plugin/bridge/interface.h
new file mode 100644
index 00000000000..062adb7ea51
--- /dev/null
+++ b/yt/yql/plugin/bridge/interface.h
@@ -0,0 +1,74 @@
+#pragma once
+
+#include <unistd.h>
+
+////////////////////////////////////////////////////////////////////////////////
+
+// This is a plain C version of an interface described in yt/yql/plugin/plugin.h.
+// All strings without separate length field are assumed to be null-terminated.
+
+////////////////////////////////////////////////////////////////////////////////
+
+struct TBridgeYqlPluginOptions
+{
+    const char* MRJobBinary;
+    const char* UdfDirectory;
+
+    struct TBridgeCluster
+    {
+        const char* Cluster;
+        const char* Proxy;
+    };
+    ssize_t ClusterCount;
+    TBridgeCluster* Clusters;
+    const char* DefaultCluster;
+
+    const char* OperationAttributes;
+
+    const char* YTTokenPath;
+
+    // TODO(max42): passing C++ objects across shared libraries is incredibly
+    // fragile. This is a temporary mean until we come up with something more
+    // convenient; get rid of this ASAP.
+    using TLogBackendHolder = void;
+    TLogBackendHolder* LogBackend;
+};
+
+// Opaque type representing a YQL plugin.
+using TBridgeYqlPlugin = void;
+
+using TFuncBridgeCreateYqlPlugin = TBridgeYqlPlugin*(const TBridgeYqlPluginOptions* options);
+using TFuncBridgeFreeYqlPlugin = void(TBridgeYqlPlugin* plugin);
+
+////////////////////////////////////////////////////////////////////////////////
+
+// TODO(max42): consider making structure an opaque type with accessors a-la
+// const char* BridgeGetYsonResult(const TBridgeQueryResult*). This would remove the need
+// to manually free string data.
+struct TBridgeQueryResult
+{
+    const char* YsonResult = nullptr;
+    ssize_t YsonResultLength = 0;
+    const char* Plan = nullptr;
+    ssize_t PlanLength = 0;
+    const char* Statistics = nullptr;
+    ssize_t StatisticsLength = 0;
+    const char* TaskInfo = nullptr;
+    ssize_t TaskInfoLength = 0;
+
+    const char* YsonError = nullptr;
+    ssize_t YsonErrorLength = 0;
+};
+
+using TFuncBridgeFreeQueryResult = void(TBridgeQueryResult* result);
+using TFuncBridgeRun = TBridgeQueryResult*(TBridgeYqlPlugin* plugin, const char* impersonationUser, const char* queryText, const char* settings);
+
+////////////////////////////////////////////////////////////////////////////////
+
+#define FOR_EACH_BRIDGE_INTERFACE_FUNCTION(XX) \
+    XX(BridgeCreateYqlPlugin) \
+    XX(BridgeFreeYqlPlugin) \
+    XX(BridgeFreeQueryResult) \
+    XX(BridgeRun)
+
+////////////////////////////////////////////////////////////////////////////////