Idea: Diagnostic actions

[mrcjkb]

Feature description

Similar to hover actions, but for diagnostics.

In monorepos with multiple projects, hls will fail to start if there is an error in a subpackage the package depends on. It will show a single diagnostic containing the ghc error, including the file where the error occurred.
In this case, a diagnostic action could parse the error location and add an action for going to the error location (This might be something to improve in hls).

Additionally, hls sometimes provides code actions that can fix diagnostic issues. These could be identified and presented as diagnostic actions, too.