fix error when phpdoc param has no type

[LordSimal]

Fixes #402

This adds a new warning if a param type has no type hint instead of just bailing out due to an error

[dereuromark]

Side note
You can also use TypelessParamTagValueNode check to bail early here

            if ($valueNode instanceof InvalidTagValueNode || $valueNode instanceof TypelessParamTagValueNode) {
                if (!isset($valueNode->type)) {
                    $phpcsFile->addWarning('%s type hint is missing', $tag, 'MissingParamType', [$tokens[$tag]['content']]);
                }
                continue;
            }

Note the %s, since it can be others than param as well.