Move code to be shared between Runner and Steps to suitable location

Move code to be shared between Runner and Steps to suitable location.

• New location could be entirely new project/repo, or in https://gitlab.com/gitlab-org/step-runner/ (TBD which of these we choose).
  • The latter would probably require creating a second go module within https://gitlab.com/gitlab-org/step-runner/ to hold only the common/shared code.

Current Runner modules that should move into this location:

• !4591 (merged)
• https://gitlab.com/gitlab-org/gitlab-runner/-/tree/main/helpers/trace/internal/masker
• https://gitlab.com/gitlab-org/gitlab-runner/-/tree/main/helpers/trace/internal/tokensanitizer
• https://gitlab.com/gitlab-org/gitlab-runner/-/tree/main/helpers/trace/internal/urlsanitizer

Note: some Steps modules will similarly move.

See gitlab!144373 (merged) for dicussion and context.