add command "Restart Language Server"

[GitMensch]

... as seen in the Python extension python.analysis.restartLanguageServer.

Not a priority at all, but something to possibly consider.

Reasoning: sometimes the server seems to hang and if it doesn't restart its own (which may take some seconds to be triggered, I don't know if there are other cases when this happens apart from "server chrashed") you have three options: a command like this or a manual killing of the process tree (after you've found the correct java process) or (which will loose your undo and position history) the reload window command.

[AlexXuChen]

After doing some digging, I've found some references to a VSCode issue:

microsoft/vscode/issues/76405

I'm currently investigating, and it seems doable by simply issuing a deactivate and activate in succession, I am just encountering a weird interaction with restarting the Telemetry service.

[rgrunber]

Related to #540 .

The language server should stop on its own in most cases (client exits). If the client crashes, or is brought down abruptly, the language server may continue to run for at most 30s before finally exiting. A (hacky) solution would be to use the ErrorHandler to restart.

[GitMensch]

The only option to do so currently that seems to work is to completely close vscode, then restart it again.
I've stumbled over this when updating the vsix form 0.20 to 0.21, which provided a query by vscode to restart the window which I did, but the results from the validation were still identical - until I've completely restarted vscode.

BTW: Shouldn't a vsix update trigger a restart of the language server in any case? Should this be moved out to a new issue?

[rgrunber]

Eventually when we update to vscode-language-server node client v8 (had to revert due to lack of support in Theia), we should see if restart() works. I think Alex will be trying it out to see if it works as expected.

[GitMensch]

Sounds good - but the user-provided command can still be added in the meantime, can't it?

[AlexXuChen]

Eventually when we update to vscode-language-server node client v8 (had to revert due to lack of support in Theia), we should see if restart() works. I think Alex will be trying it out to see if it works as expected.

See the fix in #551 (comment)

[AlexXuChen]

Thanks @GitMensch for the suggestion! Apologies for the delay!