Disable tab's context menu option when unavailable.

[lilingxi01]

Description

• When focused tab is the trailing one, "close tabs to the right" option in context menu should be disabled.

Related Issue

• #572
  (Consideration 3)

Checklist

• I read and understood the contributing guide as well as the code of conduct
• My changes generate no new warnings
• My code builds and runs on my machine
• I documented my code
• Review requested

Screenshots

CleanShot.2022-05-03.at.13.20.44.mp4

[lilingxi01]

@austincondiff : I think when we are building editor-splitting behavior, we are going to assign each split a WorkspaceDocument. This "disabled" only affect on the trailing tab of current WorkspaceDocument and it should also apply to every existing WorkspaceDocument when we have multiple (under splitting). So it should be fine.