VectorTemplate has various functions that repeat themselves, only
differing in their choice of names.
This refactor begins by focusing on the personal menu and introducing
a generic getMenuData function. Hardcoded `p-personal` is replaced with
an `id` template key and `msg-label` is renamed `label`.
Future patches will simplify VectorTemplate by using this new
function.
You'll note the resulting PersonalMenu.mustache file is identical
to VectorTabs. These will be merged in I098e6921e8f7ef65dacacf09b9c25f70c945e58e
Bug: T249372
Change-Id: I5ae44a1008b065381eeff93f9fa625be5c5a9de9
PersonalMenu is the login/logout notifications etc. menu at the very
top of the Vector skin.
Bug: T239248, T240062
Change-Id: Iae224cbd838e44669a9f27e6dd303c6c3b402d41
