Revise design of conversion_dispatch

[mingxwa]

Changes

• Revised the design of conversion_dispatch. It was previously defined as a class template. After this change, it will be 2 separate classes explicit_conversion_dispatch and implicit_conversion_dispatch.
• proxy won't compile with GCC 11 or 12 anymore after this change. "README" and pipelines are updated accordingly.
• Revised documentation and unit tests accordingly.

Copilot reviewed 10 out of 25 changed files in this pull request and generated 2 suggestions.

Files not reviewed (15)

• proxy.h: Language not supported
• samples/basic_facade_builder/add_convention.cpp: Language not supported
• docs/conversion_dispatch.md: Evaluated as low risk
• docs/conversion_dispatch/accessor.md: Evaluated as low risk
• docs/conversion_dispatch/operator_call.md: Evaluated as low risk
• docs/PRO_DEF_FREE_DISPATCH.md: Evaluated as low risk
• docs/explicit_conversion_dispatch.md: Evaluated as low risk
• docs/explicit_conversion_dispatch/accessor.md: Evaluated as low risk
• docs/operator_dispatch/accessor.md: Evaluated as low risk
• docs/operator_dispatch.md: Evaluated as low risk
• README.md: Evaluated as low risk
• docs/specifications.md: Evaluated as low risk
• .github/workflows/bvt-gcc.yml: Evaluated as low risk
• docs/PRO_DEF_MEM_DISPATCH.md: Evaluated as low risk
• docs/PRO_DEF_FREE_AS_MEM_DISPATCH.md: Evaluated as low risk

Comments skipped due to low confidence (3)

docs/implicit_conversion_dispatch/accessor.md:14

• [nitpick] The phrase 'return-type-of' is used without being defined. Consider defining it or using a more standard term.

using accessor<F, C, Os>::operator return-type-of<Os>...;

docs/explicit_conversion_dispatch/operator_call.md:5

• The placeholder /* see below */ is not clear and should be replaced with the actual implementation or a more descriptive placeholder.

/* see below */ operator()(T&& value) noexcept;

docs/explicit_conversion_dispatch/operator_call.md:8

• [nitpick] The return description is ambiguous. It should clearly state what the function returns and under what conditions.

Returns a value that is implicitly convertible to any type `U` with expression `U{std::forward<T>(value)}` when `T` is explicitly convertible to type `U`.

[guominrui]

implicit_conversion_dispatch?