Move Ci::Processable::Dependencies to Ci::BuildDependencies

What does this MR do?

Related to #209070 (closed)

In !27326 (merged) I've extracted all logic related to calculating job dependencies into a dedicated class Ci::Processable::Dependencies.

I originally had chosen to nest it under Ci::Processable because I though that we would want to being able to calculate job dependencies also for Ci::Bridge jobs. It turns out that it's not the case, at least not yet.

In this MR I'm moving Ci::Processable::Dependencies to Ci::BuildDependencies as currently we use dependencies only for Ci::Build jobs.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team