Add FileUpload.php file to fix autoloading

[ob-stripe]

r? @brandur-stripe @remi-stripe
cc @stripe/api-libraries

Adds a FileUpload.php file so that PSR-4 autoloading for the \Stripe\FileUpload class works correctly.

Fixes the issue reported by @ruudk in #520 (comment).

I can't think of a way to write automated tests for this, but I've verified manually that it works:

• before the fix:

php > require("vendor/autoload.php");
php > echo class_exists('Stripe\FileUpload');
php > echo class_exists('Stripe\File');
1
php > echo class_exists('Stripe\FileUpload');
1

• after the fix:

php > require("vendor/autoload.php");
php > echo class_exists('Stripe\FileUpload');
1

[brandur-stripe]

Nice! I was following along on the thread, and it's great to have found a solution so quickly.

LGTM.

[ob-stripe]

Thanks @brandur-stripe! All credit goes to @ruudk here :)

[ob-stripe]

Released as 6.19.4.

[ruudk]

Thanks for fixing it so quickly