[SwitchDeclarationSniff] Handle nested switch

[VincentLanglet]

This fix the issue reported here: #2800
I added tests.

Edit: Also close #3192

[VincentLanglet]

Friendly ping @jrfnl @gsherwood.

This PR was working for

switch ($foo) {
    case 1:
        switch ($bar) {
            case 1:
                return;
            default:
                return;
        }
    case 2:
        return 2;
}

But not for

switch ($foo) {
    case 1:
        switch ($bar) {
            case 1:
                return;
            default:
                throw new \Exception();
        }
    case 2:
        return 2;
}

After more investigation, it seems that the T_COLON of default has a scope_opener value and the scope_closer is the index of the throw token. So findStartOfStatement is returning new because it's the first token after a scope_closer.

Seems like the same happens with

switch ($foo) {
    case 1:
        switch ($bar) {
            case 1:
                return;
            default:
                return 3;
        }
    case 2:
        return 2;
}

Here findStartOfStatement is returning 3 because the T_RETURN token is the scope closer of the T_COLON of default.

So I made a minimal reproducer:

switch ($foo) {
    case 1:
        return 2;
}

When using findStartOfStatement on the token 2, it return the index of the token 2 instead of the index of the token return.

I made an issue to fix to relate this: #3192

And I added a commit we should fix the issue.

[gsherwood]

Thanks a lot for writing that code to check all the branches. Looks to work nicely.

Thanks for fixing that bug in findStartOfStatement() as well. I'm a bit surprised it's never been a problem before.