Exclude the implicit prelude import (#2798)

[ChristophHochrainer]

This PR has the following changes:

• create a constant function to document the "import (implicit) Prelude"- Prefix
• exclude an import that starts with "import (implicit) Prelude" inside minimalImportsRule
• closes Unexpected import (implicit) Prelude code lens #2798

Before this PR changes:

After this PR changes:

[pepeiborra]

Thanks! Normally I would ask for a test documenting the issue and proving the fix, but I think that this plugin doesn't have a testsuite.