[8.x] add Str::betweenAll()

[SjorsO]

This PR adds a Str::betweenAll() method:

$string = <<<STR
Follow your order with <a href="http://example.com/t&t">Track & Trace</a>

Or <a href="http://example.com/unsub">unsubscribe</a> forever.
STR;

Str::betweenAll($string, 'href="', '"'); // ['http://example.com/t&t', 'http://example.com/unsub']

My use-case is that I want to visit the first link from an email in a Dusk test. I intercept the email, and have to get the first link. With this new method I can do so using Str::betweenAll($email->body, 'href="', '"')[0].

This new method is similar to Str::between():

Str::between('[a]', '[', ']') // 'a'
Str::betweenAll('[a]', '[', ']') // ['a']

Str::between('[a] [b]', '[', ']') // 'a] [b'
Str::betweenAll('[a] [b]', '[', ']') // ['a', 'b']

[foremtehan]

return Collection imo

[taylorotwell]

Thanks for your pull request to Laravel!

Unfortunately, I'm going to delay merging this code for now. To preserve our ability to adequately maintain the framework, we need to be very careful regarding the amount of code we include.

If possible, please consider releasing your code as a package so that the community can still take advantage of your contributions!

If you feel absolutely certain that this code corrects a bug in the framework, please "@" mention me in a follow-up comment with further explanation so that GitHub will send me a notification of your response.