Align project and personal snippet abilities

What does this MR do?

Allow developers to use overloaded snippet ability names instead of type specific names. For example can?(:edit_snippet) or can?(:edit_snippet, @project) instead of can?(:edit_personal_snippet) and can?(:edit_project_snippet, @project).

Rather than alias the ability names I have changed them everywhere in the code. While aliasing would have been much easier, we would end up with two systems rather than one.

Screenshots

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

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

Closes #39087 (closed)