Fix polygon stroke vertex deduplication

[ICOM725]

This PR

• Fixes a bug

Describe the changes below:

Compare consecutive stroke vertices in the same coordinate space. The existing check compares the current origin-adjusted vertex with the previous unadjusted vertex, which can skip distinct corners or retain duplicate vertices when the display origin is non-zero.

Add regression tests for the centered diamond in #7361, consecutive duplicate vertices with zero and non-zero display origins, and open paths.

Fixes #7361.

Validation:

• The new tests reproduce the bug before the fix (3 failed, 1 passed).
• npm test -- tests/gameobjects/shape --maxWorkers=2: 320 tests passed.
• npm run build: webpack compilation passed; the optional copy-to-examples step reports a missing sibling examples directory.
• Targeted ESLint 8.57.1 checks passed for both changed files using the repository configuration and test globals.
• git diff --check passed.

The repository's npm run lint command fails to load its legacy JSON configuration with the installed ESLint 10 (ERR_IMPORT_ATTRIBUTE_MISSING). No dependency or lint configuration changes are included.