feat(router): add "paramsInheritanceStrategy" router configuration option

Previously, the router would merge path and matrix params, as well as
data/resolve, with special rules (only merging down when the route has
an empty path, or is component-less). This change adds an extra option
"paramsInheritanceStrategy" which, when set to 'always', makes child
routes unconditionally inherit params from parent routes.

Closes #20572.

tools/public_api_guard/router/router.d.ts

@@ -127,6 +127,7 @@ export interface ExtraOptions {
     errorHandler?: ErrorHandler;
     initialNavigation?: InitialNavigation;
     onSameUrlNavigation?: 'reload' | 'ignore';
+    paramsInheritanceStrategy?: 'emptyOnly' | 'always';
     preloadingStrategy?: any;
     useHash?: boolean;
 }
@@ -329,6 +330,7 @@ export declare class Router {
     readonly events: Observable<Event>;
     navigated: boolean;
     onSameUrlNavigation: 'reload' | 'ignore';
+    paramsInheritanceStrategy: 'emptyOnly' | 'always';
     routeReuseStrategy: RouteReuseStrategy;
     readonly routerState: RouterState;
     readonly url: string;