Improve WebGL font error message to suggest textFont() usage

[yugalkaushik]

Improves the error message when rendering text in WebGL mode without properly setting a font.

Problem:
The current error "only Opentype (.otf) and Truetype (.ttf) fonts are supported" is misleading when users have loaded a valid font but forgot to call textFont().

Solution:
Added clarification: "Make sure to set the font using textFont() before drawing text."

PR Checklist

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

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Thank You!

[ksen0]

If the test runs, then this sounds reasonable and helpful! I checked the failing test and I'm not sure what was up, I reran. If it fails, then code would need to be updated so tests do pass.

Minor wording revision to keep the message same length:

WEBGL: requires Opentype (.otf) or Truetype (.ttf) font, loaded using textFont() before drawing text.

cc @davepagurek @perminder-17