vello_hybrid: paint external textures through the regular image paint path

[nicoburns]

Summary

This follows up #109. With vello_gpu 0.3, external textures are an ordinary image paint (ImageSource::external_texture, linebender/vello#1824). So anyrender_vello_hybrid no longer needs to treat them as a special case.

• anyrender_paint_to_vello_hybrid_paint now maps Paint::Resource(ImageBrush<ResourceId>) to PaintType::Image(ImageBrush { image: ImageSource::external_texture(id, full_texture_rect, true), sampler }). It looks the texture up in texture_bindings and falls back to transparent when there is no binding.
• fill no longer has its own Paint::Resource branch. Textures now work for fill, stroke and draw_glyphs (and so inside layers too), as they already did for the vello backend.
• The whole ImageBrush is now used: sampler extend modes, quality and alpha, plus brush_transform on any shape.
• Behaviour change: with brush_transform: None, the texture is now anchored at the shape's coordinate origin. Before, it was anchored at the shape's bounding-box origin. This matches anyrender_vello. Blitz custom widgets (e.g. examples/wgpu_texture) fill a rect at (0, 0), so they are unaffected.
• draw_glyphs now calls reset_paint_transform(). Previously, glyph paints could inherit a stale brush_transform left over from an earlier fill or stroke.

No public API changes. WebGL is unchanged, since it has no texture bindings.

Link to Devin session: https://dioxus.staging.devinenterprise.com/sessions/45dbc6c083354777aaa43442ce8ef8ab
Open in Devin Desktop: https://dioxus.staging.devinenterprise.com/desktop/session/45dbc6c083354777aaa43442ce8ef8ab?variant=devin-insiders
Requested by: @nicoburns

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