Move direction semantics from dispatches to conventions

[mingxwa]

Motivation

Dereferencing a pointer with std::to_address() is feasible, but throws away cv-ref qualifiers. It is acceptable in many cases, but has certain limitations comparing to std::move_only_function (C++23) and std::copyable_function (C++26). Therefore, we have made a major decision to switch from std::to_address() to operator* when dereferencing a pointer that is potentially qualified. Consequently, we also decided to remove the direction semantics in reflection types (added in #121) because the result type of operator* relies on the qualifier of a pointer.

Changes

• Revised semantics of concept facade.
• Removed constraints on reflection types.
• Moved check for field static constexpr bool is_direct from dispatch types to convention types.
• Changed dependent type of proxy_invoke from the combination of dispatch and overload types into one convention type.
• Changed dependent type of access_proxy from an instantiation of proxy into one facade type.
• Added operator* to proxy.
• Added operator* to the 3 pointer implementations: inplace_ptr, allocated_ptr and compact_ptr.
• Added another two APIs in facade_builder: add_indirect_convention and add_direct_convention. The existing add_convention is equivalent to add_indirect_convention.
• Removed DIRECT and INDIRECT macros of dispatch definition introduced in Implement indirection syntax #121, specifically:

PRO_DEF_INDIRECT_MEM_DISPATCH(__NAME, ...)
PRO_DEF_DIRECT_MEM_DISPATCH(__NAME, ...)
PRO_DEF_INDIRECT_FREE_DISPATCH(__NAME, ...)
PRO_DEF_DIRECT_FREE_DISPATCH(__NAME, ...)
PRO_DEF_INDIRECT_OPERATOR_DISPATCH(__NAME, ...)
PRO_DEF_DIRECT_OPERATOR_DISPATCH(__NAME, ...)
PRO_DEF_INDIRECT_PREFIX_OPERATOR_DISPATCH(__NAME, ...)
PRO_DEF_DIRECT_PREFIX_OPERATOR_DISPATCH(__NAME, ...)
PRO_DEF_INDIRECT_POSTFIX_OPERATOR_DISPATCH(__NAME, ...)
PRO_DEF_DIRECT_POSTFIX_OPERATOR_DISPATCH(__NAME, ...)
PRO_DEF_INDIRECT_CONVERSION_DISPATCH(__NAME, ...)
PRO_DEF_DIRECT_CONVERSION_DISPATCH(__NAME, ...)