fix: Make Tween work with continuous target changes

[TheSpeedM]

Description

Fixes #14849 by adjusting when this.#current.v is read in Tween.set, getting the behavior more in line with the (now deprecated) tweened. See the issue for demos illustrating the problem.

I couldn't think of an appropriate test for this. As this is my first PR for Svelte, any help or feedback would be greatly appreciated!

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[changeset-bot]

🦋 Changeset detected

Latest commit: 287a3bd

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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svelte	Patch

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[TheSpeedM]

Should I fix the other issue I am having with Tween (#14897) in this PR or should I create a seperate PR?

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@14895

[dummdidumm]

Thank you! Makes sense to me, but waiting on @Rich-Harris for another pair of eyes

[Rich-Harris]

thank you!

[dummdidumm]

@TheSpeedM feel free to open a separate PR for #14897