Throw exception when calling NestedArray::setValue() when parents reference a non-array value instead of causing a PHP error

Checked ConfigTest and this was the only instance of expectError().

NestedArray::setValue() already has some support for this but allowed the error to happen; we can catch it before it happens and throw an exception instead.

Given this is a component I think we should update \Drupal\Tests\Component\Utility\NestedArrayTest to test for this too.

Added test coverage to the component, also uncovered an existing bug where $force was not required if you were replacing a scalar directly with an array - this now triggers a LogicException without $force, which I think is the correct behaviour.

Appears to have caused large number of test failures.

This is changing the behavior of NestedArray so I think another solution is needed. And it also prevents installing Drupal thus the many failed tests.

Yeah maybe the behaviour is intended although it seemed wrong when I wrote the test, I will just write another test instead and not change the behaviour I think...

Reverted behaviour change, fixed the test. I guess it's by design that you can overwrite a scalar with an array, just you can't try to make further children under the scalar that previously didn't exist.

Feedback and tests appear to be added.

Committed 1c017c0 and pushed to 11.x. Thanks!
Committed e8ac11d and pushed to 10.3.x. Thanks!

11.x commit didn't make it to the repo.