cpp/ranges/subrange/deduction guides

These deduction guides are provided for std.

@1@ Deduces the template arguments from the type of iterator and sentinel. The is sized if  is satisfied, as determined by the default template argument.

@2@ Deduces the template arguments from the type of iterator and sentinel, while the size of range is specified. The is always sized.

@3@ Deduces the template arguments from the type of range. The is sized if the size can be obtained from the range or its iterator and sentinel.

@4@ Deduces the template arguments from the type of range, while the size of range is specified. The is always sized.

The exposition-only alias template maps each integer-like type to its corresponding unsigned version.