fix(fill-style): correct pattern orientation by flipping texture y-axis (Fixes #10548)

[waterWang]

Fix pattern orientation in FillStyleExtension

Problem

FillStyleExtension renders patterns flipped vertically (top-to-bottom) compared to the original asset. A line pattern going from bottom-left to top-right (/) appears as bottom-right to top-left (\).

Root cause

The texture coordinate system has y=0 at the bottom (OpenGL convention), but the geometry coordinates have y increasing upward. When computing texCoords from patternUV (which is derived from geometry coordinates), the y-axis was not flipped, causing the pattern to appear inverted.

Fix

Flip the y-axis of patternUV when computing texture coordinates:
```glsl
// Before
vec2 texCoords = fill_patternBounds.xy + fill_patternBounds.zw * patternUV;

// After
vec2 texCoords = fill_patternBounds.xy + fill_patternBounds.zw * vec2(patternUV.x, 1.0 - patternUV.y);
```

Breaking change

This fix changes the visual output of FillStyleExtension for all users who rely on the current (incorrect) pattern orientation. The issue author noted this is a breaking change, but the fix aligns the rendering with the principle of least surprise — patterns should render in the same orientation as the original asset.

Closes #10548

[chrisgervang]

Thanks. Please include unit tests and a screenshot from the website example to validate this addresses the issue.

[chrisgervang]

Hey @Pessimistress, this is a breaking change so my recommendation is approving but waiting for v10. Wdyt? #10548 seems valid

[coveralls]

coverage: 84.119%. remained the same — waterWang:fix/fill-style-extension-pattern-flip into visgl:master

[Pessimistress]

@chrisgervang I think it's acceptable to make a breaking change if it's correcting wrong behavior.

@waterWang have you tested OrthographicView with flipY:true (top-left y)? Both configurations should render to the same orientation.

[Pessimistress]

Please add a note to docs/upgrade-guide.md

[greptile-apps]

Greptile Summary

This PR corrects vertically mirrored FillStyleExtension patterns by reversing the pattern-space y coordinate before sampling the texture atlas.

• Changes texture-coordinate calculation from patternUV to vec2(patternUV.x, 1.0 - patternUV.y).
• Leaves atlas bounds, placement, opacity, masking, and texture upload behavior unchanged.

Confidence Score: 5/5

The PR appears safe to merge, with no concrete functional, security, or repository-rule issues identified.

The atlas uses top-origin frame coordinates, and neither bounds generation nor texture upload performs a y-axis inversion, so applying the flip at sampling time consistently corrects the rendered pattern orientation.

Important Files Changed

Filename	Overview
modules/extensions/src/fill-style/shader-module.ts	Correctly flips the pattern-local y coordinate during atlas sampling, with no conflicting flip elsewhere in the established texture path.

_{Reviews (1): Last reviewed commit: "Merge branch 'master' into fix/fill-styl..." | Re-trigger Greptile}