feat(router): add unmatchedInputBehavior option to componentInputBinding

Introduce a new configuration option `unmatchedInputBehavior` to the `componentInputBinding` feature. This option allows users to configure the behavior when a component input is not matched by any key in the router data.

The available values are:
- 'alwaysUndefined': (Default) Always binds undefined to unmatched inputs.
- 'undefinedIfStale': Binds undefined only if the input was previously available in the router data for the active route in the outlet.

This feature addresses concerns raised in #63835 and #52946 regarding the retention of default values for inputs that were never targeted by the router, while still ensuring that stale data is cleared when a parameter is removed.

adev/src/content/guide/routing/common-router-tasks.md

@@ -66,6 +66,28 @@ Use `ComponentInputBindingOptions` to disable query parameter binding if you man
 provideRouter(appRoutes, withComponentInputBinding({queryParams: false}));
 ```
 
+### Configure behavior for inputs not available in router data
+
+By default, the router sets an input to `undefined` if it was not available in the router data during a navigation. This ensures that stale data is not retained.
+
+If you want to avoid setting `undefined` for inputs that have _never_ been available in the router data for the active component instance, you can set the `unmatchedInputBehavior` option to `'undefinedIfStale'`:
+
+```ts
+provideRouter(appRoutes, withComponentInputBinding({unmatchedInputBehavior: 'undefinedIfStale'}));
+```
+
+When you combine `unmatchedInputBehavior: 'undefinedIfStale'` with `queryParams: false`, inputs retain their initial values unless they are explicitly provided by the router. The exception is matrix parameters: if a matrix parameter is provided in one navigation and removed in a subsequent one, the router will set the input to `undefined` to avoid retaining stale data.
+
+```ts
+provideRouter(
+  appRoutes,
+  withComponentInputBinding({
+    queryParams: false,
+    unmatchedInputBehavior: 'undefinedIfStale',
+  }),
+);
+```
+
 ### Inherit parent route data
 
 By default, child routes inherit parameters and data from parent routes (equivalent to `paramsInheritanceStrategy: 'always'`). This means you can access parent route info directly in child components.