ApplyWorkspaceEditResponse should contain a reason for why the edit was not applied

[DanTup]

When sending an applyEdit request to the client, it can respond with a ApplyWorkspaceEditResponse that has a boolean field named applied:

	/**
	 * Indicates whether the edit was applied or not.
	 */
	applied: boolean;

There is no field for the client to supply a reason why the edit failed (for example, was it that the version of the document was wrong? did the edit reference invalid files? did it contain invalid positions?) which could make it difficult to track down when something goes wrong.

[dbaeumer]

Good point. That would be easy to add via a PR. The reason however should be optional.