ResourceVariables shouldn't need twice the memory when initializing.

This is safe because all ops which write to resource variables check whether
there are other outstanding references to the buffer and copy if that's the
case. So we can safely reuse the buffer of initializer tensors even in weird
cases such as initializing from a constant (which should never be mutated)
or using the same tensor to initialize multiple variables.

PiperOrigin-RevId: 206211065