struct CancelRequest

The `cancel` request is used by the client in two situations:

- to indicate that it is no longer interested in the result produced by a

specific request issued earlier

- to cancel a progress sequence.

Clients should only call this request if the corresponding capability

`supportsCancelRequest` is true. This request has a hint characteristic: a

debug adapter can only be expected to make a 'best effort' in honoring this

request but there are no guarantees. The `cancel` request may return an error

if it could not cancel an operation but a client should refrain from

presenting this error to end users. The request that got cancelled still

needs to send a response back. This can either be a normal result (`success`

attribute true) or an error response (`success` attribute false and the

`message` set to `cancelled`). Returning partial results from a cancelled

request is possible but please note that a client has no generic way for

detecting that a response is partial or not. The progress that got cancelled

still needs to send a `progressEnd` event back.

A client should not assume that progress just got cancelled after sending

the `cancel` request.