Improve type inference inside loops

[momala454]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce

function world(string $a): void
{
}

/** @param array<string> $a */
function hello(array $a): void
{
    $bestValue = null;
    foreach ($a as $test) {
        if ($bestValue === null) {
            $bestValue = $test;
        } else {
            var_dump($bestValue);
            world($bestValue);
        }
    }
}
hello(['hello', 'world']);

Expected behavior
Type is string, not never

Screenshots

Platform and version
1.12.4

[bmewburn]

There's currently a limitation in the control flow analysis implementation. A workaround is to widen the type with an annotation.

/** @var string|null $bestValue */
$bestValue = null;