Add a command to cancel an active download #1031
Description
We need a command (similar to CDP and Playwright) that would allow clients to cancel an active download. Therefore a unique ID is needed to reference it, and which needs to be created with the browsingContext.downloadWillBegin event, and as well used in the browsingContext.downloadEnd event.
Further we can then extend the browser.close command to not prompt for a user decision on if the running downloads should be canceled or not. Or we define that we always cancel without a decision (as what we have or beforeunload prompts) given that this is a prompt which might not appear by all browsers and is not a usual user prompt as opened by the content process.
CC @sadym-chromium and @gsnedders. Do you force the browser not to open this prompt in case it would usually appear on shutdown?