bug: manually entering project directory is laggy due to checking remote path

When connecting to a Coder workspace, users have the option to change the project directory by entering a path in a text field.

This text field appears to periodically validate the remote path, but this can happen in the middle of typing a new path.

https://github.com/coder/jetbrains-coder/assets/4949514/8f21b45c-20a8-4880-9158-bccd149476a3

It also appears to happen sync in the application thread, with the result that input will appear to periodically 'lag' while the remote path is checked.

This should ideally be done completely in the background, and when the user stops typing inside the text field.