JSCBC-1369: MutateIn Replace with empty path should do a full doc replace

Motivation
----------
The RFC states that on a mutateIn Replace with an empty spec, the SDK should
d oa full doc replace

Changes
-------
Change the opcode to a SET_DOC when an empty path is provided onto a replace mutateIn spec

Change-Id: Id862f3fa7e64a72ff2d69122bdbbdafe7a278809
Reviewed-on: https://review.couchbase.org/c/couchnode/+/234798
Reviewed-by: Jared Casey <jared.casey@couchbase.com>
Tested-by: Mateusz <matt.wozakowski@couchbase.com>

Author: Matt-Woz

lib/sdspecs.ts

@@ -408,12 +408,14 @@ export class MutateInSpec {
     value: any | MutateInMacro,
     options?: { xattr?: boolean }
   ): MutateInSpec {
-    return this._create(
-      binding.protocol_subdoc_opcode.replace,
-      path,
-      value,
-      options
-    )
+    let opCode = binding.protocol_subdoc_opcode.replace
+
+    // On an empty path we replace the whole document
+    if (path.length === 0) {
+      opCode = binding.protocol_subdoc_opcode.set_doc
+    }
+
+    return this._create(opCode, path, value, options)
   }
 
   /**