RFR: 8332895: Support interpolation for backgrounds and borders [v36]

[Michael Strauß]

On Sat, 14 Sep 2024 07:02:33 GMT, Nir Lisker <nlisker at openjdk.org> wrote:

>> Interpolation with `null` is not possible: `Interpolatable.interpolate(T, double)` is specified to throw NPE when `null` is passed in. When a styleable property transitions from a null value to a non-null value, it always transitions as discrete (i.e. is switches at the 50% mark) and doesn't use `Interpolatable.interpolate`.
>
> So when will these checks fail?

They will never fail as currently implemented. I just added them as documentation for future maintainers.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1522#discussion_r1759684905