build(docs-infra): implement the 'package' API template (#24631)

PR Close #24631

packages/animations/PACKAGE.md

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+Implements a domain-specific language (DSL) for defining web animation sequences for HTML elements as
+multiple transformations over time.
+
+Use this API to define how an HTML element can move, change color, grow or shrink, fade, or slide off
+the page. These changes can occur simultaneously or sequentially. You can control the timing of each
+of these transformations. The function calls generate the data structures and metadata that enable Angular
+to integrate animations into templates and run them based on application states.
+
+Animation definitions are linked to components through the `{@link Component.animations animations}`
+property in the `@Component` metadata, typically in the component file of the HTML element to be animated.
+The `trigger()` function encapsulates a named animation, with all other function calls nested within. Use
+the trigger name to bind the named animation to a specific triggering element in the HTML template.
+
+Angular animations are based on CSS web transition functionality, so anything that can be styled or
+transformed in CSS can be animated the same way in Angular. Angular animations allow you to:
+
+* Set animation timings, styles, keyframes, and transitions.
+* Animate HTML elements in complex sequences and choreographies.
+* Animate HTML elements as they are inserted and removed from the DOM, including responsive real-time
+  filtering.
+* Create reusable animations.
+* Animate parent and child elements.
+
+Additional animation functionality is provided in other Angular modules for animation testing, for
+route-based animations, and for programmatic animation controls that allow an end user to fast forward
+and reverse an animation sequence.
+
+@see Find out more in the [animations guide](guide/animations).
+@see See what polyfills you might need in the [browser support guide](guide/browser-support).