Disable "Build" button if configuration is already in progress

Clicking on "Build" while configuration is in progress results in an error message. Maybe it would make sense to just disable all actions that cannot be performed during this process and instead indicating what's going on with the option to cancel it?

Start by tracing the Build action and the configuration-in-progress state in the VS Code CMake Tools extension. Determine which actions are unavailable during configuration and how cancellation is currently exposed. Done means Build and other invalid actions are disabled while configuration runs, with a clear indication and a way to cancel if supported.

Written by the indexing model from the issue text.