[Php85] Skip nested compound assignment in ArrayFirstLastRector

[Soean]

Description

ArrayFirstLastRector rewrites $array[array_key_last($array)][0] += 1 to array_last($array)[0] += 1. array_last() returns a value rather than a reference, so the compound assignment writes into a temporary and is discarded, silently:

$a = [[0, 0, 0]];
array_last($a)[2] += 5;          // $a[0][2] stays 0
$a[array_key_last($a)][2] += 5;  // $a[0][2] becomes 5

shouldSkip() checks IS_ASSIGN_OP_VAR, but AssignedToNodeVisitor sets that attribute only on the outermost node of the assignment target. For $array[$key][0] += 1 that is the outer dim fetch, while the rule matches the inner one, so the guard does not apply. The plain assignment form was already skipped through PHPStan's Scope::isInExpressionAssign(), which is why the existing skip_as_assign_op fixture did not catch this.

Fix

AssignedToNodeVisitor now marks the whole dim fetch chain, which reflects what the assignment does: $array[$key][0] += 1 writes to $array[$key] as well. ArrayDimFetchToMethodCallRector reads the same attribute and benefits too.

Fixtures for both the compound and the plain nested form are added.

[TomasVotruba]

Thank you