Allow specifying $parent / $parents

[ondrejmirtes]

We should be able to specify the type of $parent and $parents[X] with a new annotation <!-- ko-... -->.

It's important for KOLint to understand what can be in $parent, $parents[0] (same as $parent allegedly), $parents[1] etc...

[tscpp]

$parent should be typed automatically when possible, e.g. with, foreach, let, etc.. And asserting the $parent should be workaround for when the inferred type doesn't work (e.g. custom binding handlers).