Fix issue #7400 - Issue with mouseX and mouseY when using a CSS border

[HarshitaKatariya]

Resolves #7400

Changes:

• Fixed the issue with mouseX and mouseY not accounting for CSS borders on the canvas.
• Added offset correction logic using getBoundingClientRect() in the manual test example: example_3_2.js.

Screenshots of the Change:

N/A

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PR Checklist

• npm run lint passes
• Inline documentation is included / updated
• Unit tests are included / updated

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