11daf6ceb1 More Span simplifications (Pieter Wuille)
568dd2f839 Replace MakeSpan helper with Span deduction guide (Pieter Wuille)
Pull request description:
C++17 supports [user-defined deduction guides](https://en.cppreference.com/w/cpp/language/class_template_argument_deduction), allowing class constructors to be invoked without specifying class template arguments. Instead, the code can contain rules to infer the template arguments from the constructor argument types.
This alleviates the need for the `MakeSpan` helper. Convert the existing MakeSpan rules into deduction rules for `Span` itself, and replace all invocations of `MakeSpan` with just `Span` ones.
ACKs for top commit:
MarcoFalke:
re-ACK 11daf6ceb1 Only change is removing a hunk in the tests 🌕
Tree-SHA512: 10f3e82e4338f39d9b7b407cd11aac7ebe1e9191b58e3d7f4e5e338a4636c0e126b4a1d912127c7446f57ba356c8d6544482e47f97901efea6a54fffbfd7895f
8b1de78577