Add an indicator for the current window

[heycalmdown]

for #12997

[msftclas]

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[coveralls]

Coverage remained the same at 61.233% when pulling bcfc586 on heycalmdown:current-indicator into 602155b on Microsoft:master.

[bpasero]

@heycalmdown thanks for the PR, can we maybe try to play with the description property instead? Here is how it works code wise:

return <IPickOpenEntry>{
    label: w.title,
    description: (id === w.id) ? nls.localize('current', "Current Window") : void 0,
    run: () => {
        ipc.send('vscode:showWindow', w.id);
    }
};

and here is how it would look like:

[heycalmdown]

Clearer. Thanks.

[coveralls]

Coverage remained the same at 61.233% when pulling e8c8407 on heycalmdown:current-indicator into 602155b on Microsoft:master.