Add keycode fes warning

[a-y-a-n-das]

Resolves #7876

Changes:

• Added a one-time Friendly Error System (FES) warning for keyCode usage in src/core/main.js.
  • The warning informs users that keyCode is deprecated and suggests using keyIsDown() instead.
• Added a manual test files: test/manual-test-examples/events/keyCode-warning.html and test/manual-test-examples/events/keyCode-warning-sketch.js
  • Verifies that the warning appears once and key behavior remains unchanged.

Screenshots of the change:

PR Checklist

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

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Thank You!

[a-y-a-n-das]

Hi!
I realized I should’ve claimed this issue first (as per the contributing guidelines), but since it wasn’t assigned to anyone and was still open, I went ahead and fixed it.
Hope that’s okay — please review when you get a chance. I can make any necessary adjustments if needed. 😊

[a-y-a-n-das]

@ksen0, let me know if any changes are needed.

[a-y-a-n-das]

Hi @ksen0, just a gentle follow-up on this PR.
Please let me know if there’s anything I should update or adjust to help move it forward.
Thanks, and I appreciate your time.

[ksen0]

Hi @a-y-a-n-das thanks for making the PR! Sorry it fell through the cracks (part of the purpose of "wait for assignment" policy is to avoid missing these, since there are hundreds of notifications). Will take a look in the next days.

[ksen0]

@a-y-a-n-das actually before digging further I see already this PR targets the v1 branch (previously it was main), but should target main (previously it was 2.0). Please check the original issue discussion, the problem is specifically about version 2.x