Adopt C++20 ranges in the code

Once #4378 merges, we'll be able to use C++20 features. Among these features is [range support](https://en.cppreference.com/w/cpp/ranges.html), which would simplify various operations we perform on standard containers.

Start by checking prerequisite issue #4378 and reviewing the C++20 ranges reference linked in the issue. Then survey the standard-container operations in the codebase to identify suitable replacements. Done means adopting ranges where appropriate after #4378 merges while preserving existing behavior.

Written by the indexing model from the issue text.