Merge #20429: refactor: replace (sizeof(a)/sizeof(a[0])) with C++17 std::size

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 🌩

Tree-SHA512: b01d32c04b9e04d562b7717cae00a651ec9a718645047a90761be6959e0cc2adbd67494e058fe894641076711bb09c3b47a047d0275c736f0b2218e1ce0d193d

src/util/strencodings.h

@@ -17,8 +17,6 @@
 #include <string>
 #include <vector>
 
-#define ARRAYLEN(array)     (sizeof(array)/sizeof((array)[0]))
-
 /** Used by SanitizeString() */
 enum SafeChars
 {