Future Breaking Changes

[joshwooding]

This is an umbrella issue to track changes for v2.

### Breaking Changes - AG-Grid Theme
- [ ] Remove `.editable-numeric-cell`

### Breaking Changes - Core
- [ ] Remove `separators` prop from `FlexLayout`
- [ ] #1335
- [ ] Card `interactive` prop
- [ ] Default style injection to false #2532
- [ ] Navigation Item: Remove wrapping `<div/>` so that NavigationItem renders either a `<button\>` or `<anchor/>`, this will enable us to pass `...rest` to the actual `<button\>` or `<anchor/>`, rather than to the wrapping `<div/>`. The breaking change is the Typescript types and the `ref`, which currently a `<div/>` . This change is now possible due to us adding a more customisable API through the `render` prop. #3417
- [ ] Remove `UNSTABLE_` backwards compatibility
- [ ] ViewportProvider #3265
- [ ] Use of `@media (hover: hover)`
- [ ] Formalize `--saltComponent-xyz` API (vs `--componet-xyz`)
- [ ] Investigate potential inclusion mentioning CSS layer, depends on whether minimum browser support can be bumped?

### Breaking Changes - Theme
- [ ] Remove deprecated tokens

### Breaking Changes - Dependencies
- [ ] Bump up [minimum browser support](https://www.saltdesignsystem.com/salt/about/supported-platforms#browser)