Refactor HarmonyRouterDelegate pages property

[GikuyuNderitu]

The HarmonyRouterDelegate's pages prop is currently composed of a messy if/else decision structure to declarative routing structure of the application. Instead of this structure, provide a Map data structure that maps defined a defined HarmonyPage enum to a given PageBuilder where PageBuilder is defined as:

typedef PageBuilder = Page Function<T extends PageBuilderArguments>(T);