e829c9afbf refactor: replace sizeof(a)/sizeof(a[0]) by std::size (C++17) (Sebastian Falbesoner)
365539c846 refactor: init vectors via std::{begin,end} to avoid pointer arithmetic (Sebastian Falbesoner)
63d4ee1968 refactor: iterate arrays via C++11 range-based for loops if idx is not needed (Sebastian Falbesoner)
Pull request description:
This refactoring PR picks up the idea of #19626 and replaces all occurences of `sizeof(x)/sizeof(x[0])` (or `sizeof(x)/sizeof(*x)`, respectively) with the now-available C++17 [`std::size`](https://en.cppreference.com/w/cpp/iterator/size) (as [suggested by sipa](https://github.com/bitcoin/bitcoin/pull/19626#issuecomment-666487228)), making the macro `ARRAYLEN` obsolete.
As preparation for this, two other changes are done to eliminate `sizeof(x)/sizeof(x[0])` usage:
* all places where arrays are iterated via an index are changed to use C++11 range-based for loops If the index' only purpose is to access the array element (as [suggested by MarcoFalke](https://github.com/bitcoin/bitcoin/pull/19626#discussion_r463404541)).
* `std::vector` initializations are done via `std::begin` and `std::end` rather than using pointer arithmetic to calculate the end (also [suggested by MarcoFalke](https://github.com/bitcoin/bitcoin/pull/20429#discussion_r567418821)).
ACKs for top commit:
practicalswift:
cr ACK e829c9afbf: patch looks correct
fanquake:
ACK e829c9afbf
MarcoFalke:
review ACK e829c9afbf 🌩
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cd66d8b1d8