Add support for LaTeX enviroments

[maikol-solis]

Expected Behavior

If the user enables mixed-pitch-mode (https://gitlab.com/jabranham/mixed-pitch), it's expected that the latex enviroments were fontified in fixed-font

Actual Behavior

However, right now, there are fontified in variable-font

Steps to Reproduce

1. Enable mixed-pitch-mode for markdown-mode
2. Just open a markdown file with some latex environment.

Backtrace

Looking at the text properties, the issue is markdown-mode confuses the latex environment with italics.

Software Versions

• Markdown Mode: 2.6-alpha
• Emacs: 29.1
• OS: MacOS

[maikol-solis]

I have the same issue.