This reverts merge request !27276

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.

The JobArtifact is required to retrieve the creation date

Switch from read_project_security_dashboard to read_vulnerability
Since it's a main policy. read_project_security_dashboard should
be used only for dashboard policy

The /api/v4/project/:id/vulnerabilities is going
to be used for serving the new Vulnerability model
instances for First-class Vulnerabilities feature.
The previous behavior (responding with
Vulnerabilities::Occurrence) is moved to
/api/v4/project/:id/vulnerability_findings path
unconditionally (regardless of the feature flag).
This is a breaking change.

Extract Vulnerabilities API into a separate module
and implement GET projects/:id/vulnerabilities API
operation. Respect :first_class_vulnerabilities
feature flag.

Extract Vulnerabilities API into a separate module
and implement GET projects/:id/vulnerabilities API
operation. Respect :first_class_vulnerabilities
feature flag.

Use Vulnerabilities::OccurrencesPreloader for API requests

Vulnerabilities API results can now be limited to a given pipeline.

Previously, Vulnerabilities API would return all however it should only
return non-dismissed by default. This behavior can be changed with
`scope=all`

Adds API endpoint for returning all vulnerabilities for a given project