Modal,Backdrop - Add animation support

Is this a new component or an extension?

Enhancement to a current feature

Existing Component

Modal, Backdrop

Describe the feature

Modal & Backdrop animation support

• See related issue: https://github.com/patternfly/patternfly-react/issues/12519

PatternFly Modals (and Backdrop that it uses) currently lack a smooth animation from closed->open->closed states.
This works well for smaller modals showing simple information or requiring a simple action from the user; But for larger modals it is really jarring.

A proposed new component <Tearsheet> that leverages the <Modal> makes this missing animation a larger friction point with a near-full-screen modal size.

Modal and Backdrop could function like the other PF components that already opt-in to animations via <AnimationsProvider>. opt-in is important to not break or regress the performance of pages depending on the as-is of Modals/Backdrops.

User Story

As a user, when I use a Modal with rich information or a form, it is jarring to see it flash on screen with no visual easing from the open-to-closed state.

Visuals & Mockups

https://github.com/user-attachments/assets/644f9584-d227-41ef-b0b4-7c6b7fd2eb09

Interaction States & Variations

• On opening: modal fades in + shifts down a few pixels slightly and falls full into view

• On closing: modal fades out + shifts up a few pixels slightly and is removed from view

Accessibility (A11y)

No response

Product & Target Release

No response

Contribution

• I am interested in contributing this feature.

• I have searched for similar existing requests.

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Jira Issue: PF-4419