P2278R4 `cbegin` Should Always Return A Constant Iterator

[StephanTLavavej]

P2278R4 cbegin Should Always Return A Constant Iterator

Feature-test macro (expected):

#define __cpp_lib_ranges_as_const 202207L

[JMazurkiewicz]

I'm working on this feature.

• "Span" section (P2278R4: cbegin should always return a constant iterator ("Ranges" and "Span" sections) #3187)
• "Iterators" section (P2278R4: cbegin should always return a constant iterator ("Iterators" section only) #3043)
• "Range" section (P2278R4: cbegin should always return a constant iterator ("Ranges" and "Span" sections) #3187)
• "As const view" section (P2278R4: views::as_const #3234)
• LWG-3765 (P2278R4: cbegin should always return a constant iterator ("Iterators" section only) #3043)
• LWG-3766 (P2278R4: cbegin should always return a constant iterator ("Ranges" and "Span" sections) #3187)
• LWG-3811 (P2278R4: views::as_const #3234)