Scale image from center in HeroImageFlowDelegate

[yunusemrebakir]

Description

This PR modifies the _HeroImageFlowDelegate class to scale the image from the center instead of the top left corner.

Problem

The hero image was scaling from the top left corner and this was causing the image to look not-centered.
To fix this, we now scale the image from the center.

In the updated code, we calculate the translationX and translationY values to shift the image by half of the difference between the container size and the scaled image size. Then, we create a Matrix4 object using Matrix4.identity() and apply both the scaling and translation using the scale and translate methods respectively. Finally, we pass the resulting transformMatrix to the transform property of flowPaintingContext.paintChild.
With this modification, the image should be scaled from the center instead of the top left.

Screenshots

Phone

Before	After

Tablet

Before	After