support "showOutput" flag in task config

[elaihau]

Description

In VS Code there is a showOutput flag we can use to toggle if task output should show up in the terminal
https://stackoverflow.com/a/38723286

In Theia we should implement the same thing to achieve the same user experiences.

Reproduction Steps

Run any task in Theia. The task output shows up in the terminal.

OS and Theia version:

Ubuntu 18.04. master branch as of Aug 16 2019. Example browser

[westbury]

This is related to #5597 . That PR exposes output on the frontend but does not dictate where it goes, so it can go to, for example, a progress monitor, output channel, or a problem marker generator. Remember that Theia is extendable whereas VS Code is not, so while a toggle may be appropriate for VS Code, the ability to rebind API is more useful for Theia extenders.

[vince-fugnitto]

The showOuput flag has been deprecated for a while now (since 1.14 in VS Code) and was replaced by the reveal property. I believe we can safely close the issue as reveal provides even more options for end-users.

definitions.showOutputType.deprecationMessage = nls.localize(
	'JsonSchema.tasks.showOputput.deprecated',
	'The property showOutput is deprecated. Use the reveal property inside the presentation property instead. See also the 1.14 release notes.'
);