Closes the file buffer (as if member close was called), and then acquires the contents of rhs.
rhs is a closed buffer after the call with an otherwise unspecified but valid state.
It is unspecified whether the internal sequence is the one in rhs before the call, or a copy of it. In any case, both objects use independent sequences after the call (if any).
A filebuf object of the same type (with the same class template parameters charT and traits), whose internals are moved.
Modifies both filebuf objects (*this and rhs).
Concurrent access to the same file stream buffer objects may introduce data races.
Basic guarantee: if an exception is thrown, the file stream buffer is in a valid state.