Report usage of .save and StripeClient

[richardm-stripe]

Changelog

• Reports uses of the deprecated .save and of StripeClient in X-Stripe-Client-Telemetry. (You can disable telemetry via \Stripe\Stripe::setEnableTelemetry(false);, see the README.)

Details

I've added usage to several infrastructure methods:

• Several underscored methods in lib/ApiOperations/Request.php. (Since they are underscored, they should not be considered part of the public interface). I've included a default value there for expedience sake, though. Most callsites for these methods have no usage to report.
• request and requestStream in ApiRequestor. These are public, but I have added a default value so that it is non-breaking.
• The private _requestRaw and _requestRawStreaming in ApiRequestor. No default value here, but they are private.
• The RequestTelemetry constructor which is public (but I doubt it has much external use), but I've added a default value there.
• I've modified BaseStripeClient to always pass in through ["stripe_client"] as usage to ApiRequestor, and modified ->save in ApiOperations to pass in ["save"] through to the helpers in Request.php.

Testing

I modified the existing test case for telemetry to use a method that would trigger "save" usage to be included. It mocks at the HTTP Client level, which is fine, because all the logic for telemetry is thankfully implemented at a higher level of abstraction in ApiRequestor.