Configurable cursor animation trail strength

[tiny-paris]

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I've noticed some feedback on the recently added cursor animation (#63195) that the Neovide-style trail can feel a bit too strong or distracting, especially with block cursors and high-contrast themes.

I'm thinking about adding a configurable trail_strength setting, ranging from 0.0 to 1.0:

• 0.0 — Smooth cursor movement without deformation, similar to the JetBrains-style animation.
• 0.5 — A more subtle trail with less stretching.
• 1.0 — The current Neovide-inspired animation, unchanged.

The default would remain 1.0, so existing users wouldn't see any difference unless they explicitly changed the setting.

I'd also like to show the trail strength option in the Settings UI only when cursor animation is enabled.

Implementation-wise, I think this should be possible within the existing editor animation code, without requiring changes to GPUI.

Would this be a welcome addition to the existing cursor animation feature?