Use consistent approach to create TipTap editor in tests

What does this MR do?

Tests in the Content Editor often need an instance of the TipTap Editor class. Also, this class is often difficult to instantiate because it requires a small set of extensions to function properly. Over the last 3 milestones, we’ve come up with several approaches for instantiating this class in test specs. This MR brings consistency to the Content Editor specs by narrowing the approaches to one.

Screenshots (strongly suggested)

This MR does not introduce user-facing changes.

Does this MR meet the acceptance criteria?

Conformity

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Availability and Testing

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Security

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• 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
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