Preserve lineGradientStyle in SWF shape exports

[Tutez64]

SWFShape.export() already emits lineGradientStyle(...) for LINESTYLE2 records that use a gradient fill, but ShapeCommandExporter inherited the no-op implementation from DefaultShapeExporter. As a result, Animate/SWFLite exports kept the base lineStyle but lost the gradient stroke data.

This adds LineGradientStyle to shape commands and wires it through:

• ShapeCommandExporter
• Animate serialization/deserialization
• Animate shape rendering
• SWFLite shape rendering

SWFLineGradientStyleExportRepro.zip

[Tutez64]

Added LineGradientStyle handling in:

• swf.runtime.Shape
• swf.runtime.MorphShape

Both now forward the command to graphics.lineGradientStyle(...), matching the Animate and SWFLite renderers and fixing the test failures.

Also fixed the AIR/Flash error by casting line gradient color arrays to Array<UInt> under #if flash, matching the existing beginGradientFill handling. I applied the same cast to the Animate and SWFLite render paths so LineGradientStyle behaves consistently across exporters.