refactor: Easing function names + typo fix

[timrodz]

I've been working with this library on a project, and noticed that easing functions can be named since they come from a specific source. Also fixed a typo 🌱

packages/core/src/data/constants.ts

• Creates string literal type EASING
• Modifies the type definition for EASINGS to be a Record<EASING, ...> instead of Record<string, ...>

packages/core/src/utils/animation.ts

• Fixes typo for interpoaltion -> interpolation
• Fixes missing doc link {@link CONSTANTS.EASINGS} -> {@link EASINGS}

Benefit: When interacting with CONSTANTS.EASINGS a developer can now get intellisense for which functions are available - Also applies to those using this library in their own projects

Merge request checklist

• All lints and tests pass. If needed, new tests were added.
• If needed, the documentation has been updated.

[github-actions]

This feature/bug fix has been released in version 5.14.1.