Review and consolidate components

This repo has three sets of reusable "generic" components:

• src/generic
• src/editors/sharedComponents
• src/files-and-videos/generic

These components have a bunch of issues:

1. Redundancy with each other. Some examples are listed here but there are more. These should either be consolidated or one of them renamed to clarify the difference.

   • AlertError and ErrorAlert seem very similar.
   • PromptIfDirty and usePromptIfDirty are identical except one is a hook. We don't need both, or the component could be simplified to wrap the hook.
   • CodeEditor and CodeEditor
   • FileInput and FileInput
   • more; this isn't a complete list

2. Some things are "temporary" workarounds for Paragon bugs that should no longer be needed

   • SelectableBox should be replaced with the upstream Paragon version. (see old explanation why this happened)
   • src/generic/NewsstandIcon.tsx

3. It's unclear why some of them exist or how they should be used, like this repo's own version of Button. A style guide page or storybook type resource should explain all the reusable studio widgets, and the code should have JSDoc comments with a clear justification for each one.

4. Each part of this MFE - course outline, unit page, advanced settings, pages & resources, libraries, taxonomy editor, editor modals - has a totally different look and feel. We should use a library of standard Studio UX patterns & components for a more consistent look & feel.

   • Here's how a unit looks on the course outline:
     
   • Here's how the same unit looks in the search modal:
     
   • Here's how a unit looks in the library:
     

5. Some things, if they're that useful, should perhaps be moved to upstream Paragon or an Open edX component library ??

This is a large umbrella, so create sub-issues as needed.

Start by inventorying src/generic, src/editors/sharedComponents, and src/files-and-videos/generic, comparing the listed AlertError, PromptIfDirty, CodeEditor, FileInput, SelectableBox, NewsstandIcon, and Button entries. Review their usage and the Paragon replacement before splitting this umbrella into focused sub-issues. Done should be defined by the resulting sub-issues: consolidated or clearly renamed components, documented reusable widgets, and consistent Studio patterns.