fix(addon-image): disable desynchronized resize canvas

[SergioChan]

Summary

• Image addon currently creates layer canvases with { desynchronized: true }.
• During resize this can show blank-frame jitter on some platforms because repaint may miss the resize frame.
• Switch layer canvas creation to { desynchronized: false } so resize and repaint stay synchronized.

Fixes #5691.

Validation

• npm run lint -- addons/addon-image/src/ImageRenderer.ts

[Tyriar]

Need to test this on Windows before and after to verify it's fixed.

[SergioChan]

Thanks — I ran a Windows before/after check as requested.

Environment:

• Windows 10 (22H2)
• Chrome (stable)
• xterm.js demo page (image addon, snake sample)

What I tested:

1. Before: local baseline with desynchronized: true in ImageRenderer.ts
2. After: this PR version with desynchronized: false
3. Repeated rapid resize loops between narrow/wide viewport sizes + manual drag-resizing.

Result:

• I could not reproduce visible jitter/blank-frame behavior in my Windows environment in either baseline or patched variant.
• So from this machine I can’t provide a “before jitters / after fixed” confirmation yet.

If you have a specific repro setup (GPU/browser flags/display scale/steps) where you can reproduce reliably, I can rerun exactly that path and report back with targeted results.

[Tyriar]

Let's put this on hold until I can test on the machine I know I saw it on then.