[TSL] Refactor snappy implementation and introduce resize_uninitialized.

This change moves platform specific snappy implementations to tsl/platform/snappy.cc, removing duplicate code.

Additionally, STLStringResizeUninitialized is moved from tensor_cord.cc to tsl/lib/strings/resize_uninitialized.h to be used by snappy.cc and tensor_cord.cc.

PiperOrigin-RevId: 821467924

Author: majnemer

tsl/platform/snappy.h

@@ -16,7 +16,8 @@ limitations under the License.
 #ifndef TENSORFLOW_TSL_PLATFORM_SNAPPY_H_
 #define TENSORFLOW_TSL_PLATFORM_SNAPPY_H_
 
-#include "xla/tsl/platform/types.h"
+#include <cstddef>
+#include <string>
 
 #if !defined(PLATFORM_WINDOWS)
 #include <sys/uio.h>
@@ -25,21 +26,18 @@ using ::iovec;  // NOLINT(misc-unused-using-decls)
 }  // namespace tsl
 #else
 namespace tsl {
-struct iovec {
-  void* iov_base;
-  size_t iov_len;
-};
+using ::snappy::iovec;
 }  // namespace tsl
 #endif
 
 namespace tsl {
 namespace port {
 
 // Snappy compression/decompression support
-bool Snappy_Compress(const char* input, size_t length, string* output);
+bool Snappy_Compress(const char* input, size_t length, std::string* output);
 
 bool Snappy_CompressFromIOVec(const struct iovec* iov,
-                              size_t uncompressed_length, string* output);
+                              size_t uncompressed_length, std::string* output);
 
 bool Snappy_GetUncompressedLength(const char* input, size_t length,
                                   size_t* result);