[8.x] Define route regular expression constraints

[gregorip02]

This allows us to define constraints for routes using whose regular expression is sometimes repetitive.

Instead of having something like this

<?php

Route::get('/articles/{user}/{slug}')->where(['user' => '[0-9]+', 'slug' => '[A-Za-z]+']);

We would have something simpler like this.

<?php
Route::get('/articles/{user}/{slug}')->whereNumber('user')->whereAnyChar('slug');

Regular expression constraint methods added

<?php

Route::get('/posts/{post}')->whereNumber('post');

Route::get('/posts/{post}')->whereAnyChar('post');
Route::get('/posts/{post}')->whereLowerChar('post');
Route::get('/posts/{post}')->whereUpperChar('post');

Route::get('/search/{search}')->whereSlash('search');

[taylorotwell]

The general idea is not bad but I'm not I understand whereSlash... maybe I don't understand the naming. I'm also not sure whereLowerChar and whereUpperChar would be very useful.