Replace the hand-rolled let _x / getX / __resetX boilerplate with the
createSingleton helper in all nine remaining singleton stores. Exposed
accessor names (getX, __resetX) are unchanged, so consumers and specs are
unaffected. Teardown wired to each stores destroy() where it has one
(fontCatalog, fontLifecycle, typography, availableFilter, theme, layout,
scrollBreadcrumbs); sort and appliedFilter have no teardown. Also merges
layoutStores duplicate $shared/lib imports.
Ilia Mashkov
fe07c60dd4