Honour Application abstract contract in ReportServiceProvider

Summary:
Laravel Container and so Application classes offer to access services:

• using the make method in the abstract contract
• through ArrayAccess in the concrete implementation

We used array access, but documented ReportServiceProvider::register
is happy to accept any \Illuminate\Contracts\Foundation\Application.

To honour this claim, we so switch to use the make method.

This is a follow-up to 6ed92b9a75b8.

This fixes the following phan issue:

app/Providers/ReportServiceProvider.php:21
PhanTypeArraySuspicious
Suspicious array access to \Illuminate\Contracts\Foundation\Application

Test Plan: Run tests

Reviewers: dereckson

Reviewed By: dereckson

Subscribers: alken-orin

Differential Revision: https://devcentral.nasqueron.org/D771