Simple array access
-----
<?php

$a['b'];
$a['b']['c'];
$a[] = $b;
$a{'b'};
${$a}['b'];
-----
array(
    0: Expr_ArrayDimFetch(
        var: Expr_Variable(
            name: a
        )
        dim: Scalar_String(
            value: b
        )
    )
    1: Expr_ArrayDimFetch(
        var: Expr_ArrayDimFetch(
            var: Expr_Variable(
                name: a
            )
            dim: Scalar_String(
                value: b
            )
        )
        dim: Scalar_String(
            value: c
        )
    )
    2: Expr_Assign(
        var: Expr_ArrayDimFetch(
            var: Expr_Variable(
                name: a
            )
            dim: null
        )
        expr: Expr_Variable(
            name: b
        )
    )
    3: Expr_ArrayDimFetch(
        var: Expr_Variable(
            name: a
        )
        dim: Scalar_String(
            value: b
        )
    )
    4: Expr_ArrayDimFetch(
        var: Expr_Variable(
            name: Expr_Variable(
                name: a
            )
        )
        dim: Scalar_String(
            value: b
        )
    )
)