fix(talk): preserve whitespace in markdown code blocks

[eatyourgreens]

Style Markdown code blocks so that long lines wrap without collapsing whitespace.

Trim comments so that comments with leading whitespace aren't accidentally displayed as code blocks.

• Fixes #6686 by styling code blocks with pre-wrap, not pre-line.
• Fixes #1599 by trimming leading whitespace from Talk comments.
• Fixes #7113 by applying Talk comment styles to inbox messages.

Test cases to run locally:

• Planet Four comments with leading whitespace that are accidentally displayed as code blocks: https://local.zooniverse.org:3735/projects/mschwamb/planet-four-terrains/talk/29/3494/?comment=6783&env=production&page=1
• Markdown tests on staging: https://local.zooniverse.org:3735/talk/38/372
• a Talk comment with a Python script: https://local.zooniverse.org:3735/talk/18/3317233?comment=5524608&env=production

Talk discussions:

• Message Lines Not Wrapping

Required Manual Testing

• [ ] Does the non-logged in home page render correctly?
• [ ] Does the logged in home page render correctly?
• [ ] Does the projects page render correctly?
• [ ] Can you load project home pages?
• [ ] Can you load the classification page?
• [ ] Can you submit a classification?
• [ ] Does talk load correctly?
• [ ] Can you post a talk comment?

Review Checklist

• [ ] Does it work in all major browsers: Firefox, Chrome, Edge, Safari?
• [ ] Does it work on mobile?
• [ ] Can you npm ci and app works as expected?
• [ ] If the component is in coffeescript, is it converted to ES6? Is it free of eslint errors? Is the conversion its own commit?
• [ ] Are the tests passing locally and on GitHub Actions?

Optional

• [ ] Have you replaced any ChangeListener or PromiseRenderer components with code that updates component state?
• [ ] If changes are made to the classifier, does the dev classifier still work?
• [ ] Have you resized and compressed any image you've added?
• [ ] Have you added in flow type annotations?
• [ ] Have you followed the Springer guidelines for commit messages?