[10.x] Change newPendingRequest() method from protected to public

[pascalbaljet]

This PR makes the newPendingRequest() method on the HTTP Client Factory publicly accessible. This way, you can instantiate a new PendingRequest class with the Global Middleware applied, as there's no other way to get the Global Middleware from outside of the factory.

The PendingRequest class is used by Saloon's Laravel Plugin, but it currently lacks support for Global Middleware because it can't access the $globalMiddleware array. See also saloonphp/laravel-http-sender#15.

If this change is not desired, I could also submit an alternative PR that simply adds a getGlobalMiddleware() method to the HTTP Client Factory.

[pascalbaljet]

Closed as this is a breaking change.