LSP Progress support should take care of cancellable

[angelozerr]

In LemMinx maven we have supported LSP progress when local artifacts are loaded:

It works great but:

• the progress monitor display a stop button altough the lemminx maven says that it is not cancellable
• when I click on the stop button it stops the progress bar but it doesn't cancel the lemminx maven process. I think LSP4E should cancel the LSP progress future.