In order to allow users to create shapes with fill but no visible
border/stroke (Closes #7020), this PR adds a `'none'` value to
`DefaultDashStyle`. When the dash style is set to `'none'`, shapes
render their fill normally but skip all stroke/border rendering. Shape
indicators still work correctly for selection purposes.

The `'none'` dash style is not exposed in the UI style panel — it can
only be set programmatically via the SDK.

### Change type

- [x] `feature`

### Test plan

1. Create a geo shape (rectangle, ellipse, etc.) and set dash style to
`'none'` programmatically
2. Verify the shape fill renders but no border/stroke is visible
3. Verify the shape is still selectable (indicator appears on
hover/select)
4. Test with draw shapes — closed draw shapes with fill should show fill
but no stroke
5. Test with arrow shapes — arrow body should be hidden with none dash
6. Test with line shapes — line should be invisible but still selectable
7. Test SVG export with none dash — exported SVG should have no stroke
8. Test x-box geo shape — the internal X lines should not render with
none dash

- [ ] Unit tests
- [ ] End to end tests

### Release notes

- Add `'none'` dash style option that hides shape borders while
preserving fill

### API changes

- Added `'none'` to `DefaultDashStyle` enum values (`TLDefaultDashStyle`
type)
- Added `NonePathBuilderOpts` interface for the none style in
`PathBuilder`
- `PathBuilder.toSvg()` now returns `null` for `'none'` style
- `PathBuilder.toPath2D()` returns empty `Path2D` for `'none'` style

### Code changes

| Section         | LOC change |
| --------------- | ---------- |
| Core code       | +41 / -11  |
| Automated files | +15 / -9   |

---------

Co-authored-by: huppy-bot[bot] <128400622+huppy-bot[bot]@users.noreply.github.com>