fix: Allow Backspace and Delete keys in WASM Skia TextBox/PasswordBox

[Copilot]

• Understand the issue: Backspace key not working on WASM Skia for PasswordBox and sometimes TextBox on Android
• Identify root cause in BrowserInvisibleTextBoxViewExtension.ts
• Fix the onkeydown handler to not prevent Backspace and Delete key default behavior
• Build and test the fix locally - Build succeeded
• Verify no regressions in existing tests - Tests passed
• Address review feedback: Exclude Ctrl/Cmd+Backspace/Delete from browser handling to preserve word deletion functionality
• Include Alt modifier check for macOS Option+Backspace/Delete word deletion

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[WASM Skia] Backspace key does not work (TextBox, PasswordBox)</issue_title>
<issue_description>### Current behavior 🐛

Backspace soft keyboard key on Android never works on PasswordBox and sometimes does not work on TextBox. The easiest way to reproduce textbox failing is to enter text with spaces in it into a textbox and then try to backspace it:

Screen_Recording_20260104_222621_One.UI.Home.mp4

This was tested with Material theme but probably applies to all themes.

Expected behavior 🎯

Backspace button should work.

How to reproduce it (as minimally and precisely as possible) 🔬

No response

Workaround 🛠️

No response

Renderer 🎨

• Skia
• Native

Affected platforms 📱💻🖥️

WebAssembly

Uno.Sdk version (and other relevant versions) 📦

6.4.53, 6.5.0-dev.100

IDE version 🧑‍💻

No response

Anything else we need to know? 💬

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [WASM Skia] Backspace key does not work (TextBox, PasswordBox) #22230

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[Copilot]

Pull request overview

This PR fixes a critical bug where the Backspace key was not functioning correctly in TextBox and PasswordBox controls on WASM Skia, particularly affecting mobile soft keyboards on Android. The fix modifies the TypeScript keyboard event handler to allow Backspace and Delete keys to use the browser's default behavior rather than preventing it, ensuring that text deletion operations trigger properly through the oninput event.

Key Changes

• Modified the onkeydown handler in BrowserInvisibleTextBoxViewExtension.ts to allow Backspace and Delete keys to pass through
• Added early return logic before preventDefault() call for these specific keys
• The browser's default behavior will now handle text deletion and propagate changes via the oninput event to managed code

[Jen-Uno]

@copilot issue is solely with Android.

[unodevops]

🤖 Your WebAssembly Skia Sample App stage site is ready! Visit it here: https://unowasmprstaging.z20.web.core.windows.net/pr-22277/wasm-skia-net9/index.html

[unodevops]

🤖 Your Docs stage site is ready! Visit it here: https://unodocsprstaging.z13.web.core.windows.net/pr-22277/docs/index.html

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

[unodevops]

🤖 Your WebAssembly Skia Sample App stage site is ready! Visit it here: https://unowasmprstaging.z20.web.core.windows.net/pr-22277/wasm-skia-net9/index.html

[unodevops]

🤖 Your Docs stage site is ready! Visit it here: https://unodocsprstaging.z13.web.core.windows.net/pr-22277/docs/index.html

[jeromelaban]

This issue needs to be tested manually before being merged.