Intellisense tooltip applies text formatting on source code

[MikhailArkhipov]

microsoft/vscode-python#2225

Environment data

• VS Code version: 1.25.1
• Extension version (available under the Extensions sidebar): 2018.7.0
• OS and version: Windows 10
• Python version (& distribution if applicable, e.g. Anaconda): 3.7.0
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): venv
• Relevant/affected Python packages and their versions: NA

Actual behavior

The tooltip applies text formatting to the displayed code, e.g. wrapping text in underscores italicizes it.

Expected behavior

The tooltip shows the code as it is written in the source.

Steps to reproduce:

1. Use the mypy linter
2. Define a variable in a class, using self, with underscores in its name
3. Assign a type to the variable with a type hint
4. Hover over it to see the Intellisense tooltip

[jakebailey]

Fixed in #596 and others.

Generated tooltips from signatures will be enclosed in literal blocks, and docstrings should be properly escaped.