Add fontWidth() and clarify textWidth vs fontWidth docs in attributes.js

[NalinDalal]

Resolves #7745

This pull request introduces a new user-facing function, fontWidth(), to the p5.js library and updates the documentation to clearly distinguish between advance width and tight bounding box measurements for text. All changes are made in src/typography/attributes.js.

Changes

• New Function:
  • fontWidth() returns the advance width (loose measurement) of a string, including all leading and trailing whitespace, as measured by the browser's measureText().width.
• Documentation Updates:
  • Added comprehensive JSDoc and usage examples for fontWidth().
  • Updated textWidth() documentation to clarify that it returns the tight bounding box width, which may ignore leading/trailing whitespace.
  • Both docs now include a direct comparison, cross-references, and clear examples to help users choose the correct function.
• No changes to p5.Font.js:
  • All documentation and code changes are limited to attributes.js as per maintainer feedback.

Motivation

• Addresses confusion in p5.js 2.0 about the difference between textWidth() and the new fontWidth() regarding whitespace handling.
• Provides clear, side-by-side documentation for both functions to help users understand which measurement to use.
• Implements feedback from maintainers to keep documentation changes only in attributes.js.

Example Usage

let s = '   x y   ';
let advance = fontWidth(s); // includes all whitespace
let tight = textWidth(s);   // may ignore whitespace

Related Issues

• Resolves: [GitHub issue about textWidth vs fontWidth whitespace handling]

Checklist

• Added new function fontWidth()
• Updated documentation and examples in attributes.js
• No changes to p5.Font.js
• All changes on dev-2.0 branch

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This PR ensures p5.js 2.0 users have clear, accurate, and maintainers-aligned documentation for text measurement functions.

PR Checklist

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