fix(android): restore asset loading functionality to android (fix: #846)

[lily-mosquitoes]

Implements WebViewAssetLoader to load assets from the asset folder in Android when with_asset_loader is called in the builder. The function also sets the desired protocol for use in with_url, although the url must always be <protocol>://assets/<path>.

Refs: #846

What kind of change does this PR introduce?

• Bugfix
• Feature
• Docs
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes
• No

Checklist

• This PR will resolve Android assets not loaded as expected with custom protocol #846
• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.
• I have added a convincing reason for adding this feature, if necessary
• It can be built on all targets and pass CI/CD.

Other information

I am willing to provide an update to the wry template in tauri-mobile showcasing the correct form of asset loading on Android.

[wusyong]

Hey I didn't have time to review this week, but it's on my todo list. I'll find some time to review it next week.

[wusyong]

LGTM! I'll fix our limitation of android_fn and then merge it.

[lily-mosquitoes]

LGTM! I'll fix our limitation of android_fn and then merge it.

Awesome! Let me know how empty extra args will be handled and I can fix that part!

[amrbashir]

fixed in tauri-apps/tao#688 and will release a new tao version once it is merged

[wusyong]

Thanks again for the PR!