PR: Improve LSP support for MarkupString[] for hover requests

[andfoy]

Description of Changes

This PR prevents palantir/python-language-server#623 to break compatibility with Spyder

• Wrote at least one-line docstrings (for any new functions)
• Added unit test(s) covering the changes (if testable)

• Included a screenshot or animation (if affecting the UI, see Licecap)

Issue(s) Resolved

Fixes #

Affirmation

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and understand I am releasing the same under Spyder's MIT (Expat) license.

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@andfoy

[ccordoba12]

Thanks @andfoy! I verified this fix allows us to use the latest PyLS version (0.29.1).