[net9.0] Update default BlazorWebView host address

[github-actions]

Backport of #24884 to net9.0

Update default BlazorWebView host address

Changes the BlazorWebView host address to 0.0.0.1 to avoid incompatibility with future browser versions.

Description

There have been reports that MAUI Blazor stopped working in iOS 18 and macOS 15. This was due to BlazorWebView utilizing 0.0.0.0 as a host address, which is blocked in the latest versions of Safari. It was discovered that websites could send requests to 0.0.0.0 as a way to bypass Private Network Access, a standard that restricts websites from sending requests to servers on private networks. Chrome will block access to 0.0.0.0 starting in Chrome 129, and other browsers may soon follow.

This PR changes the default host address in BlazorWebView to 0.0.0.1, which is not blocked by browsers and is not subject to the same security risks.

Some other considered alternatives were:

1. Using localhost. This has the risk that it may interfere with other applications running on localhost. In fact, the MAUI repo's MacOS automated tests failed when we attempted localhost.
2. Using a fake host name (so the host address would be, e.g., https://blazor/). Unfortunately, this causes the browser to attempt DNS resolution, which causes the app to take longer to load.

Fixes #24363

Customer Impact

Without this fix, MAUI Blazor apps do not work in iOS 18 and macOS 15, and may soon stop working in Android.

Regression?

• Yes
• No

Whether the bug occurs is a factor of the browser version, not the MAUI version.

Risk

• High
• Medium
• Low

We validated manually that all WebView implementations support 0.0.0.1. Automated tests validate this as well. There is no indication that browsers will block 0.0.0.1 in the near future. In case apps are affected by this change and need to revert to using 0.0.0.0, they can do so via an AppContext switch.

Verification

• Manual (required)
• Automated

Packaging changes reviewed?

• Yes
• No
• N/A