[API] Add ZSTD_c_stable{In,Out}Buffer parameters

This commit adds the parameters and sets the value in the CCtxParams
but it does not do anything with the value.

lib/compress/zstd_compress_internal.h

@@ -238,6 +238,10 @@ struct ZSTD_CCtx_params_s {
     /* Dedicated dict search algorithm trigger */
     int enableDedicatedDictSearch;
 
+    /* Input/output buffer modes */
+    ZSTD_bufferMode_e inBufferMode;
+    ZSTD_bufferMode_e outBufferMode;
+
     /* Internal use, for createCCtxParams() and freeCCtxParams() only */
     ZSTD_customMem customMem;
 };  /* typedef'd to ZSTD_CCtx_params within "zstd.h" */