Migrate from deprecated MarkedString to MarkupContent

[krassowski]

Both hover's content and completion's documentation return a plain string:

• in the case of hover it indicates a MarkedString which is explicitly deprecated in favour of MarkupContent
• in case of completion the use of string is not deprecated, but MarkupContent is allowed and would make the transition to markdown easier in the future

MarkupContent was added in 3.3.0 (11/24/2017) which was 4 years ago and should be safe to transition now given that most clients already support much newer versions of LSP specification (usually at least 3.14).

Updating the following function to return a dictionary complying with MarkupContent interface will be sufficient:

python-lsp-server/pylsp/_utils.py

Lines 139 to 147 in 26f234a

	def format_docstring(contents):
	"""Python doc strings come in a number of formats, but LSP wants markdown.
	Until we can find a fast enough way of discovering and parsing each format,
	we can do a little better by at least preserving indentation.
	"""
	contents = contents.replace('\t', u'\u00A0' * 4)
	contents = contents.replace(' ', u'\u00A0' * 2)
	return contents

See https://github.com/krassowski/python-language-server/pull/4/files.

[ccordoba12]

I agree with this change, as long as it keeps returning plain text and not only Markdown.