Test onWillSaveTextDocument event

[jrieken]

Test for #239

• any os @chrmarti

Complexity 3

We added a new event onWillSaveTextDocument that fire before a document is saved to disk and that allows you to sneak in changes to the document. Make sure that

• the event has proper jsdoc and informs about the challenges a pre-save hook brings
• the event tells you why save happens
• the event allows to modify the document (register any long running task)
• the event allows to provide text edits that should be applied before save
• the event is protected from bad listeners (throw errors async/sync)
• the event is guarded from slow listeners (never resolve promise)

[jrieken]

FYI - to test against the latest API do the following:

• open your extensions package.json file
• change the engine.vscode property to *
• run npm run postinstall (assuming you have the vscode module as dev-dependency)
• undo the engine-version change from step 2