[vscode] extension support for generating and accept/rejecting fixes for violation(s)

[dymurray]

Our VSCode extension already makes it possible for a user to run an analysis and view the results (both in our webview and in the editor's problems panel). What we must do next is give the user the ability to ask Kai to generate a fix and render the proposed changes to the user in such a way that they can reasonable act on them (ie. accept/reject).

NOTE
There is an overlap here with the work in #58 , but we can avoid waiting for that to be fully resolved by mocking out the request/response + defining the types, and focusing our efforts on how we would render the proposed changes.