Return type declarations
-----
<?php

function test1() {}
function test2() : array {}
function test3() : callable {}
function test4() : Foo\Bar {}
-----
array(
    0: Stmt_Function(
        byRef: false
        name: Identifier(
            name: test1
        )
        params: array(
        )
        returnType: null
        stmts: array(
        )
    )
    1: Stmt_Function(
        byRef: false
        name: Identifier(
            name: test2
        )
        params: array(
        )
        returnType: Identifier(
            name: array
        )
        stmts: array(
        )
    )
    2: Stmt_Function(
        byRef: false
        name: Identifier(
            name: test3
        )
        params: array(
        )
        returnType: Identifier(
            name: callable
        )
        stmts: array(
        )
    )
    3: Stmt_Function(
        byRef: false
        name: Identifier(
            name: test4
        )
        params: array(
        )
        returnType: Name(
            parts: array(
                0: Foo
                1: Bar
            )
        )
        stmts: array(
        )
    )
)