[7.x] Add support for default values for the "props" blade tag

[Persaeus]

Currently, to make default properties for anonymous components, you have to either upgrade to a full component with a component class, or maybe do something like the following:

<!-- /resources/views/components/alert.blade.php -->

@props(['type', 'message'])
@php
    $type = $type ?? 'info'
@endphp

<div {{ $attributes->merge(['class' => 'alert alert-'.$type]) }}>
    {{ $message }}
</div>

This PR adds support for default property values that you specify in the props tag.

For the previous example, this would look something like the following:

@props(['type' => 'info', 'message'])

This benefits the user, as it's more terse and looks neater (in my opinion).

It should not conflict with how the props tag works currently, as users were not expected to pass associative or mixed arrays as arguments.

As for tests, I could not find any tests related to the props tag, so I'm no sure what I need to do.