Fix for #523

[tkshnwesper]

Description

1. It makes isFlipHorizontallyFastAnimation and isFlipVerticallyFastAnimation public
2. Assigns values of isFlipHorizontally and isFlipVertically respectively to isFlipHorizontallyFastAnimation and isFlipVerticallyFastAnimation

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• [x] I open this PR to the develop branch.
• [x] I have added a description of the change under [next] in CHANGELOG.md.
• [x] I ran dart format --output=none --set-exit-if-changed . and has success.

Breaking Change

Does your PR require Flame users to manually update their apps to accommodate your change?

• [ ] Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md).
• [x] No, this is not a breaking change.

[RafaelBarbosatec]

LGTM! Thanks for contribution!