List item styling in markdown-navigator

[christian-seifert-teradata]

When the markdown-navigator component is used to render lists, the styling doesn't match the material component.

Steps to reproduce the behavior:

Compare Covalent 5 with Covalent 8

Also compare to the material web component (expand the interactive demo and turn on leadingIcon)

Expected behavior
Style matches material component. Specifically we see 3 issues:

1. icon should be centered
2. Less padding between the icon and the text
3. Font size of header and description should be different from each other

[christian-seifert-teradata]

Another issue is that the font for the breadcrumbs has accidentally changed starting in Covalent v6.

This selector no longer matches:
https://github.com/Teradata/covalent/blob/main/libs/markdown-navigator/_markdown-navigator-theme.scss#L5

td-breadcrumbs .mat-button

.mat-button should be changed to .mdc-button