shared: codemod `shared/components/FileMatchChildren` `shared/components/Markdown` `shared/components/activation` components to CSS modules

Created by: gitstart-sourcegraph

Descriptions

This PR results from the global-css-to-css-modules codemod application with some manual fixes, caused by the usage of global CSS classes tied to a React component in other parts of the codebase

Refs

• SG Issue
• Gitstart Ticket

Success criteria

The stylesheets in the following directories are converted to CSS modules.

• client/shared/src/components/FileMatchChildren
• client/shared/src/components/Markdown
• client/shared/src/components/activation