docs: clarify ngDoCheck invocation behavior with OnPush strategy

The previous documentation for `DoCheck` / `ngDoCheck` implied that the
default change-detector had run on the directive itself, which is
misleading. `ngDoCheck` is actually invoked when the *parent's*
change-detector checks the directive's input bindings — meaning it fires
even for `OnPush` components whose own change detection was skipped.

Updated three places in lifecycle_hooks.ts:
- Interface description: scopes "the check" to input bindings in the
  parent template and adds an explicit OnPush callout.
- "detects changes" clarified to "detects changes to the directive's
  input bindings".
- Method description: "after the default change-detector runs" →
  "after the default change-detector has checked the directive's input
  bindings in the parent template".

Fixes #48140

(cherry picked from commit ca44055166)

packages/core/src/change_detection/lifecycle_hooks.ts

@@ -76,14 +76,19 @@ export interface OnInit {
 
 /**
  * A lifecycle hook that invokes a custom change-detection function for a directive,
- * in addition to the check performed by the default change-detector.
+ * in addition to the check performed by the default change-detector on the input
+ * bindings for this directive usage in the parent template. Note that this hook is
+ * invoked even when the directive's own change detection is skipped (e.g., with
+ * the `OnPush` change detection strategy). Developers might use this hook to
+ * implement a custom change detection strategy for some of the inputs.
  *
  * The default change-detection algorithm looks for differences by comparing
  * bound-property values by reference across change detection runs. You can use this
  * hook to check for and respond to changes by some other means.
  *
- * When the default change detector detects changes, it invokes `ngOnChanges()` if supplied,
- * regardless of whether you perform additional change detection.
+ * When the default change detector detects changes to the directive's input bindings,
+ * it invokes `ngOnChanges()` if supplied, regardless of whether you perform
+ * additional change detection.
  * Typically, you should not use both `DoCheck` and `OnChanges` to respond to
  * changes on the same input.
  *
@@ -104,7 +109,8 @@ export interface OnInit {
 export interface DoCheck {
   /**
    * A callback method that performs change-detection, invoked
-   * after the default change-detector runs.
+   * after the default change-detector has checked the directive's input
+   * bindings in the parent template.
    * See `KeyValueDiffers` and `IterableDiffers` for implementing
    * custom change checking for collections.
    *