[OptimizedFunctionGraphInfo] Move-construct the `FunctionLibraryDefinition` in `FromProto()`.
[OptimizedFunctionGraphInfo] Move-construct the `FunctionLibraryDefinition` in `FromProto()`.

Previously we made two copies of the `FunctionLibraryDefinition` (outside and inside the converted `Graph`) then erased the second copy. With this change, we directly reuse the `FunctionDef` protocol buffers loaded from the original `OptimizedFunctionGraph` proto (which can be several GB in size).
