`<ranges>`: Add missing test coverage for `ranges::view_interface::c(begin|end)`

[JMazurkiewicz]

#3187 introduced new members to ranges::view_interface: cbegin and cend. While there is small coverage for those functions in P0896R4_ranges_subrange/test.compile.pass.cpp, I believe that we should add extra assertions to each views tests (see #3350 for example).

• as_const (Testing: check c(begin|end) members of some C++23 ranges #3920),
• as_rvalue,
• adjacent (P2321R2: views::adjacent, views::pairwise #3508),
• adjacent_transform (P2321R2: views::adjacent_transform, views::pairwise_transform #3546),
• cartesian_product (P2374R4: views::cartesian_product #3561),
• chunk,
• chunk_by,
• common (Testing: Check c(begin|end) members of C++20 ranges #3612),
• drop (Improve views::drop(_while) and views::take(_while) tests #3390),
• drop_while (Improve views::drop(_while) and views::take(_while) tests #3390),
• elements (Improve views::elements tests #3350),
• empty (<ranges>: Test c(begin|end) members of range factories #3553),
• enumerate (P2164R9: views::enumerate #3472),
• filter (Testing: Check c(begin|end) members of C++20 ranges #3612),
• std::generator (not yet implemented),
• iota (<ranges>: Test c(begin|end) members of range factories #3553),
• istream (<ranges>: Test c(begin|end) members of range factories #3553),
• join (Testing: Check c(begin|end) members of C++20 ranges #3612),
• join_with,
• lazy_split,
• owning_view (Make P2415R2_owning_view/test.cpp test something #3753),
• ref_view (Testing: Check c(begin|end) members of C++20 ranges #3612),
• repeat (<ranges>: Test c(begin|end) members of range factories #3553),
• reverse (Testing: Check c(begin|end) members of C++20 ranges #3612),
• single (<ranges>: Test c(begin|end) members of range factories #3553),
• slide,
• split,
• stride (Testing: check c(begin|end) members of some C++23 ranges #3920),
• subrange (Testing: Check c(begin|end) members of C++20 ranges #3612),
• take (Improve views::drop(_while) and views::take(_while) tests #3390),
• take_while (Improve views::drop(_while) and views::take(_while) tests #3390),
• transform (Testing: Check c(begin|end) members of C++20 ranges #3612),
• zip (Testing: check c(begin|end) members of some C++23 ranges #3920),
• zip_transform (P2321R2: Added std::views::zip_transform. #3322).