Add control ideas research document for community toolkit expansion

[Copilot]

Research document proposing new SkiaSharp-based controls for the community toolkit, based on analysis of existing features, GitHub issues, and industry trends.

Proposed Controls

Prioritized by impact and implementation complexity:

• SKShimmerView — Skeleton loading animation with animated gradients
• SKRippleView — Material Design touch feedback
• SKGaugeView — Radial/linear gauges for dashboards
• SKParticleView — General particle system (snow, rain, fire, sparkles)
• SKSparklineView — Inline trend charts
• SKProgressRing — Circular progress with customizable styles
• SKGradientView — Animated mesh/conic gradients
• SKMorphView — Path-to-path morphing animations
• SKDonutChart — Pie/donut data visualization
• SKBlurView — Real-time glassmorphism effects

Document Contents

• Example XAML APIs for each control
• Use cases and implementation complexity
• Priority matrix based on community demand
• Utility feature suggestions (gradient builders, shadow helpers, animation utilities)
• Summary of community-requested Lottie improvements from open issues

Located at docs/CONTROL_IDEAS.md.

Original prompt

this repo is like a community toolkit for skiasharp. It is meant to put cool controls that are useful and functional and helpful for develpers who want to use skiasharp. Can you do some research and think about what sort of controls we could create.

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