Change canvas id to myCanvas in Path2D examples (Fixes #42155)

[satyam22i]

Description

This PR updates the <canvas> element ID used in the Path2D examples.
The previous examples used id="canvas", which can lead beginners to accidentally use a non-canvas element with the same ID, resulting in the common error:

getContext is not a function

The examples now consistently use id="myCanvas".

Motivation

Using a more specific and less generic ID helps prevent confusion for new developers.
It avoids accidental misuse of <div id="canvas"> and improves the clarity and reliability of the example code.

Additional details

• Updated the HTML <canvas> ID in both examples.
• Updated corresponding JavaScript getElementById() calls.

Related issues and pull requests

Fixes #42155

[wbamberg]

There are hundreds of these... should we try to fix them all? There doesn't seem to be a whole lot of point in just fixing one, if we think this is a big enough problem to be worth fixing at all.

[Josh-Cena]

Personally +1 that this is a problem. It's not immediately obvious where getContext comes from since we are not documenting the canvas element itself. Even just unhiding the HTML code goes a long way.