Fix/linear gradient string in tooltip

[xile611]

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🇨🇳 Chinese

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[Copilot]

Pull Request Overview

This PR fixes a bug where tooltip icons don't display correctly when the shape fill color is provided as a gradient string. The fix adds proper parsing of gradient strings using the GradientParser utility.

Key changes:

• Import GradientParser and IColor type from @visactor/vrender-core
• Add logic to detect and parse gradient strings before processing shape fill colors
• Update the condition that determines whether to use simple string fills versus gradient objects

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
packages/vchart/src/plugin/components/tooltip-handler/utils/svg.ts	Adds gradient string parsing logic to handle tooltip shape fills correctly
common/changes/@visactor/vchart/fix-linear-gradient-string-in-tooltip_2025-09-04-02-59.json	Changelog entry documenting the gradient string tooltip fix

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