Allow to provide description to environment collection API

[karrtikr]

Particularly for the Python environments, the list of environment vars can be long, hence the prompt which shows up can be too verbose:

It would be perhaps more helpful if we can provide a simple description instead of the exact changes.

cc/ Daniel Imms (@Tyriar)

[karrtikr]

This could also be extended to show up as terminal.title the first time the terminal is relaunched. Fish shell does not have a prompt variable which we could set like cmd to indicate which environment is active, which could also make use of this feature:

[Tyriar]

Proposal:

#171108

export interface EnvironmentVariableCollection extends Iterable<[variable: string, mutator: EnvironmentVariableMutator]> {
	/**
	 * A description for the environment variable collection, this will be used to describe the
	 * changes in the UI.
	 */
	description: string | undefined;
}

We probably still want a way to show the actual environment variable changes even with this description though.

[meganrogge]

It would be nice if there were a View Changes action that opened a readonly editor with the changes. That would make it very accessible

[Tyriar]

Megan Rogge (@meganrogge) I was thinking a button in the hover to toggle it, but I like your suggestion more