Clean up module imports across repo

[shravanhariharan2]

Currently, relative imports are used across all files, and barrel files are used inconsistently across modules. This makes the import statements long, verbose, and slightly difficult to maintain.

The goals of a fix should be to:

• Add barrel files to all modules, so that every class can be imported at the module level and not the file level
• Change relative imports to absolute imports using module-alias

Here is an issue that describes setting up module aliases on TypeScript so that the compiled JS also uses the aliases.