feat: fluent interface pattern on registerPlugin in Univer class

[kenny-not-dead]

close #xxx

The Univer class has a method for registering multiple plugins. It also allows for individual registration using the appropriate method, as documented in some places. It is proposed to expand the ability to use a fluent interface pattern similar to the RXJS method for registrations of the form

univer
.registerPlugin(pluginA)
.registerPlugin(pluginB)

With this approach, it can increase some of the code's readability, and what's important is that it's not a breaking change, but only an additional feature.

I demonstrated this approach using the existing example from the documents.

up to you

Pull Request Checklist

• Related tickets or issues have been linked in the PR description (or missing issue).
• Naming convention is followed (do please check it especially when you created new plugins, commands and resources).
• Unit tests have been added for the changes (if applicable).
• Breaking changes have been documented (or no breaking changes introduced in this PR).