[12.x] create new @hasStack Blade directive

[browner12]

this new @hasStack directive can be used to wrap @stack directives for conditional output depending on if the stack is empty or not. this can be useful if you want some wrapping code around the stack only if it is not empty.

@hasstack('list')
    <ul>
        @stack('list')
    </ul>
@endif

if you pass content to the stack

@push('list')
    <li>Item 1</li>
@endpush

you will get the output

<ul>
    <li>Item 1</li>
</ul>

but if nothing gets pushed, you'll get no output. this helps avoid the orphaned DOM you may have settled for previously. also helps avoid extra spacing you may have had previously due to gap styling on a parent element.

mimicked the @hasSection directive for naming.