message: Add body accessor for LaunchOp in TF device dialect to match up GraphOp and IslandOp of TF executor dialect.
  This exposes an accessor for the first block of the first region of the LaunchOp.
diff: @@ -68,6 +68,7 @@ def TfDevice_LaunchOp : TfDevice_Op<"launch",
  let regions = (region SizedRegion<1>:$body);
  let extraClassDeclaration = [{
  + Block &GetBody() { return getOperation()->getRegion(0).front(); }
  StringRef getDevice() { return device(); }
  }];
  