Generator for ActionView::TestCase

[Morriar]

As shown here ActionView test cases bring a lot of power to the test cases created by the user.

Tapioca should generate as much as possible in the DSL's RBIs.

Some related work already exists in Tapioca:

• https://github.com/Shopify/tapioca/blob/main/lib/tapioca/compilers/dsl/action_controller_helpers.rb
• https://github.com/Shopify/tapioca/blob/main/lib/tapioca/compilers/dsl/url_helpers.rb

[vinistock]

The work for the generator itself is here. However, it depends on being able to load test files (without actually executing the tests). Once applications can define how to load their test environment, we can merge the DSL compiler and start generating types for action view tests.