Replaced deprecated keyCode functionality and docs with KeyboardEvent.code & KeyboardEvent.key also updates the keyIsDown function to accept alphanumerics as parameters

[Vaivaswat2244]

Resolves #7436 and #6798

Changes:

This PR modernizes keyboard event handling by transitioning from the deprecated keyCode property to the modern KeyboardEvent.code and KeyboardEvent.key properties. This change improves keyboard input reliability and brings p5.js in line with current web standards.

• Updated keyboard event handling to use KeyboardEvent.code instead of e.which
• Added proper key tracking using _code property
• Updated keyboard constants to use modern string values
• Updated keyIsDown function to use alphanumeric as parameters

Screenshots of the change:

/preview/index.html test sketch is:

const sketch = function(p) {
      p.setup = function() {
        p.createCanvas(800, 600);
        p.textSize(16);
        p.textFont('monospace');
      };

      p.draw = function() {
        p.background(240);
        let y = 30;

        // Title
        p.fill(0);
        p.text("keyIsDown() Test", 20, y);
        y += 40;

        // Current key state
        p.text(Current key: ${p.key}, 20, y);
        y += 25;
        p.text(Current code: ${p._code}, 20, y);
        y += 25;

        // Test keyIsDown with direct codes
        p.text("Code String Tests:", 20, y);
        y += 25;
        p.text('ArrowLeft': ${p.keyIsDown('ArrowLeft')}, 40, y);
        y += 20;
        p.text('KeyA': ${p.keyIsDown('KeyA')}, 40, y);
        y += 40;

        // Test keyIsDown with single characters
        p.text("Single Character Tests:", 20, y);
        y += 25;
        p.text('a': ${p.keyIsDown('a')}, 40, y);
        y += 20;
        p.text('A': ${p.keyIsDown('A')}, 40, y);
        y += 20;
        p.text('1': ${p.keyIsDown('1')}, 40, y);
        y += 40;

        // Show current _downKeys object
        p.text("Current _downKeys object:", 20, y);
        y += 25;
        p.text(JSON.stringify(p._downKeys, null, 2), 40, y);
      };

PR Checklist

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