Rename `Faker::Show` to `Faker::Theater`

[jdcalvin]

Motivation / Background

This Pull Request has been created because of naming issues identified here: https://github.com/faker-ruby/faker/issues/2787

This PR replaces the usage of Faker::Show to be Faker::Theater for the following reasons:

1. The file was created under faker/music/show.rb but the class definition is Faker::Show At the very least the class should be name-spaced correctly as Faker::Music::Show

2. Faker::Show is ambiguous for its current usage. Faker::Music::Show would also be ambiguous. The class supports three methods: adult_musical kids_musical play that generate names for musicals and plays which all can be categorized under Theater.

Additional information

Related: https://github.com/faker-ruby/faker/issues/2787

Checklist

Before submitting the PR make sure the following are checked:

• [x] This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• [x] Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• [x] Tests are added or updated if you fix a bug, refactor something, or add a feature.
• [ ] Tests and Rubocop are passing before submitting your proposed changes.

If you're proposing a new generator:

• [x] Open an issue first for discussion before you write any code.
• [x] Double-check the existing generators documentation to make sure the new generator you want to add doesn't already exist.
• [x] You've reviewed and followed the Documentation guidelines.

[stefannibrasil]

Hi @jdcalvin we merged this Deprecator that can be used for this one as well: https://github.com/faker-ruby/faker/pull/2858

[stefannibrasil]

This one hasn't been updated in a while. It's currently being fixed here https://github.com/faker-ruby/faker/pull/2921