[PATCH 0/3] libstdc++: Implement P2548R6 (copyable function)

[Tomasz Kamiński]

This patch series implements the copyable_function as specified in P2548R6.
It also modifies implementation of move_only_funtion to avoid doulbe indirection
when constructing from other function wrappers, based on provision in
C++26 [func.wrap.general] p2. Finally we rename bits/move_only_function.h to
bits/funcwrap.h as this header now also defines copyable_function.