[GetToCode] Adds noshellEnabled/noshellVisible in CommandCodon to disable items based in WelcomeScreen

[netonjm]

This PR adds a new feature in CommandCodon to enable/disable menu items

Now we can add in the addon manigest

• noshellEnabled = "[true|false]"
• noshellVisible = "[true|false]"

and we'll disable/hidden menus when there is no shell (this is the WelcomeScreen mode)

This properties could be added to:

• Command (single or an array of items)
• Category

And in case of group the value will affect it's children.

Fixes VSTS #935559 - [Shell] Some menus should be disabled in only GTC mode

Disabling layout Command group

Disabling Debug category group

[Therzok]

Why do we need this?

[Therzok]

What commands should we actually have in GTC mode? Maybe we should actually conditionally add commands for when we only show GTC. As in, a whitelist, not a blacklist.

[Therzok]

I feel we should just declare a different extension point into which we put commands which are visible without the Ide being there.

[sevoku]

I agree with @Therzok, but I don't think that we need an additional extension point for this (would be cumbersome to maintain). A better approach would be a simple opt-in in CommandCodon.
Something like:

• noshellEnabled = "[true|false]"
• noshellVisible = "[true|false]"

or we use one prop like noshell = "disabled|disabled-visible"

could look like this to opt in to show in disabled state:

<Command     id = "MonoDevelop.Debugger.DebugCommands.DebugApplication"
 noshellEnabled = "false"
 noshellVisible = "true"
           [...]
/>

Also I wouldn't delegate the logic to the command handlers, but do it all in CommandManager. If a command has no opt-in, it wouldn't run the update handler at all but just set the appropriate values in the CommandInfo (so they get picked up correctly by the menu logic).

[Therzok]

Does this query gtk? We update command handlers in bulk, might be a bit too much to query this 40 times for a menu open on the UI thread.

[netonjm]

maybe we could cache this value in WelcomePageService