Better gradient support

[Keavon]

• Elliptical gradients (minor and major axis)
• Focal point
• Spread method (pad, reflect, repeat) (Support spread method for gradient #3953)
• Color interpolation (color-interpolation has limited browser support), we can also approximate in steps
• Independent interpolation of color and alpha
• Reusing vector data types to provide the spatial gradient control inputs

[YohYamasaki]

I would like to work on adding support for the spread method. Should I create a new sub issue?

[YohYamasaki]

Opened a PR for the spread method support. #3953