api.rb

This brings in Ruby 2.7 suport and a number of fixes:
https://github.com/ruby-grape/grape/blob/master/CHANGELOG.md

1. Move all inherited Grape::API -> Grape::API::Instance
2. Remove use of Virtus since this has been removed from Grape.
3. Extract Rack::Response from API error
4. Grape v1.2.3 pulled in a fix used in SafeFile:
https://github.com/ruby-grape/grape/pull/1844, so we no longer need
to maintain our custom type.
5. Adapt WorkhorseFile with the latest changes to make custom types work
with Grape and dry-types.
6. Ensure Array[String] is coerced properly.

The change from Virtus to dry-types now requires all strings to be
coerced to arrays. Before this was done within Virtus.

7. Coerce Array[Integer] types to arrays of integers

The change from Virtus to dry-types now requires all strings to be
coerced to arrays of integers. Before this was done within Virtus.