Align Theia task schema with vs code

[elaihau]

Description

As per https://code.visualstudio.com/docs/editor/tasks#_custom-tasks and https://code.visualstudio.com/docs/editor/tasks-appendix vs code task schema is quite different from that in Theia:

export interface CommandProperties<T = string> {
    readonly command: string;
    readonly args?: T[];
    readonly options?: object;
}

/** Configuration of a Task that may be run as a process or a command inside a shell. */
export interface ProcessTaskConfiguration<T = string> extends TaskConfiguration, CommandProperties<T> {
    readonly type: ProcessType;
    readonly windows?: CommandProperties<T>;
    readonly cwd?: string;
}

We should align them for consistent user experience.

This issue was originally brought up by @akosyakov in #5024 (comment)

It seems to work somehow. I've noticed that label and cwd is mandatory. It should not be. cwd should be a proper register variable which can be computed from the current context.

Also according to docs, cwd should be part of options, see here https://code.visualstudio.com/Docs/editor/tasks#_custom-tasks

If the task cannot be started, like cwd is missing, there is no any feedback to a user. Plus programming errors in logs.

like Anton said, a good first step would be moving cwd into options, and making label optional for configuring tasks.

Reproduction Steps

Open Theia example browser, open tasks.json, and create custom tasks in the editor.

OS and Theia version:

Theia 0.7. This issue is OS and browser version independent.

[mmx85]

Related to this topic.
The following works well in VS Code

        {
            "label": "Rebuild",
            "dependsOrder": "sequence",
            "dependsOn" : [ "Clean", "Build" ],
            "group": {
                "kind": "build"
            }
        }

But Theia IDE 1.55.0 complains that "type" and "command" are missing.