Streamline the validation of arrays of objects

This is a high-level (but low-priority) design issue, aiming at a possible refactoring, only to make the code a bit nicer.

Right now, there are many places where certain _arrays_ are validated, and the pattern that frequently appears is (in pseudocode):
```
const theArray = someObject.theArray;
if (defined(theArray)) {
if (!BasicValidator.validateArray(...)) {
result = false;
} else {
for (let i=0; i

No source files or tests are named. Start by locating BasicValidator and the existing array-validation call sites, then compare the repeated checks and element validators. Done should mean a settled design and a consistent refactoring that preserves the current validation rules.

Written by the indexing model from the issue text.