Improvements to package installer styling

[smg6511]

What changed and why

Updated and created several styles to make installer tab text (particularly the meta data type ones—change log, readme, license) more readable.

How to test

1. Run grunt build to update compiled CSS
2. In the package management area (installer), click on “Reinstall” for a few of your already-installed Extras or “Install” for new ones and take a look at the Change Log, Readme, and License tabs. Verify there's good separation between html elements and clear visual hierarchy. Be mindful that to some degree the quality of appearance is out of MODX’s hands and depends on the Extra author creating well-structured Markdown for each of these sections.
3. As an extra step or in place of the last step, edit any package’ manifest file (at core/packages/[Extra of your choice]/manifest.php) and replace the value of the readme key with the contents of the attached file below. (I did not try to place it inline here, because some of the backticks within get misinterpreted here.) Then, as above, click “Reinstall” and examine the tabs’ contents.
   example-readme.md

Related issue(s)/PR(s)

Partially resolves #16206; PR #16829 resolves the primary parsing problem.

Compatibility notes

n/a

Breaking change assessment

n/a

Test coverage

n/a for SASS

Contributors

This takes some of what @Ibochkarev did in PR #16829 as a starting point and expands upon it.

AI tool use

n/a