RFR: 8358820: Allow interpolation outside of range [0,1] [v2]

[Michael Strauß]

> JavaFX unnecessarily restricts interpolation in the following ways:
> 1. `Interpolatable` implementations often clamp intermediate values to the interpolation factor range [0,1].
> 2. `SplineInterpolator` doesn't accept Y coordinates outside of [0,1] for its control points. While this was probably done so that the computed interpolation factor doesn't exceed [0,1], the restriction goes far beyond that. For example, the following function is not representable, even though its values are all within the [0,1] range:<br>
>    <img src="https://github.com/user-attachments/assets/368b6142-052d-4ead-8a59-cbddf4a19660" width="400"/><br>
>    The following function is also not representable, but would be very useful for [bouncy animations](https://easings.net/#easeOutBack):<br>
>    <img src="https://github.com/user-attachments/assets/af02b044-ae4c-4250-b181-72178ad9f3f3" width="400"/>
> 
> Fortunately, there is no technical reason why JavaFX can't support the full range of animations that can be represented with a cubic Beziér interpolation function.
> 
> This PR includes the following changes:
> 1. The specification of `Interpolatable` is changed to require implementations to accept interpolation factors outside of [0,1].
> 2. All implementations of `Interpolatable` now correctly return intermediate values outside of [0,1].
> 3. `SplineInterpolator` now accepts control points with any Y coordinate.
> 
> Here's how the result looks like for the previously unrepresentable interpolation function `cubic-bezier(0.34, 2.2, 0.64, 1)`:<br>
> <img src="https://github.com/user-attachments/assets/72c10d0d-71b4-4bb5-b58c-ae377279b0fd" width="500"/>

Michael Strauß has updated the pull request incrementally with one additional commit since the last revision:

  javadoc

-------------

Changes:
  - all: https://git.openjdk.org/jfx/pull/1822/files
  - new: https://git.openjdk.org/jfx/pull/1822/files/85aacc4d..92d06d7e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1822&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1822&range=00-01

  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/1822.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1822/head:pull/1822

PR: https://git.openjdk.org/jfx/pull/1822