PR: Some fixes to make Spyder work with the latest changes in PyLSP

[ccordoba12]

Description of Changes

• Request documentation in plain text to the server because it sends it now by default as Markdown, which we can't handle.
• Fix error when showing completion hints due to the previous change in the server as well.
• Fix not showing hovers for objects without docstrings. Signatures that come from the server are now separated from docstrings by two LF characters, which was causing this problem.
• Update outline if a tree is empty but it has cached items from the server. I discovered this bug while working with Spyder these days and although it's not caused by a server update, I think it's important to fix it because it makes the Outline display files with no symbols when they actually have symbols to be displayed.

Affirmation

By submitting this Pull Request or typing my (user)name below,
I affirm the Developer Certificate of Origin
with respect to all commits and content included in this PR,
and understand I am releasing the same under Spyder's MIT (Expat) license.

I certify the above statement is true and correct: @ccordoba12

[ccordoba12]

@dalthviz, this needs to be removed when updating our dependencies before releasing 5.4.0.

[ccordoba12]

Also this.

[ccordoba12]

And this.

[ccordoba12]

@spyder-ide/core-developers, after this PR you need to install docstring-to-markdown in your development environments. Otherwise Spyder will crash.

[mrclary]

@spyder-ide/core-developers, after this PR you need to install docstring-to-markdown in your development environments. Otherwise Spyder will crash.

Under what circumstances with this cause Spyder to crash?
Is this not a Spyder dependency or python-lsp-server dependency?
How is this installed for end users? I only see it added to the macOS installer extra packages.

[ccordoba12]

That package is a direct dependency of PyLSP 1.6.0, which I just released. The thing is Spyder imports a little function from a PyLSP module which happens to also import docstring-to-markdown, so it'll crash if it's not installed.

[mrclary]

That package is a direct dependency of PyLSP 1.6.0, which I just released. The thing is Spyder imports a little function from a PyLSP module which happens to also import docstring-to-markdown, so it'll crash if it's not installed.

Okay. Since it's not an optional dependency (plugin) for python-lsp-server, it does not need to be specified in the macOS extra packages (although there is no harm).

[ccordoba12]

Correct. I had to add docstring-to-markdown as a requirement before releasing PyLSP 1.6.0 so that the Mac app workflow didn't fail. But @dalthviz will remove its entry tomorrow before releasing 5.4.0.