Add context for when Output is Focused / Visible

[3v1n0]

I wanted to customize my keybindings depending on the OutputPanel state, but it looks there's no clause to set in the when stanza for it.

[isidorn]

There is a context inOutput, please try that

[3v1n0]

Ok that works when if focused (but needs to be documented), what about when it's visible?

[isidorn]

We accept PRs that update our docs. Checkout the vscode-docs repo.
No this is not currently supported, we accept PRs that add this.

Code pointers
Similar to the viewlet service here
https://github.com/Microsoft/vscode/blob/master/src/vs/workbench/services/viewlet/browser/viewletService.ts#L19
The panelPart would add a context key https://github.com/Microsoft/vscode/blob/master/src/vs/workbench/browser/parts/panel/panelPart.ts#L34