Fix StringBuilder concurrency crash in JdkInfo.GetJavaProperties

[Copilot]

ProcessUtils.Exec subscribes the same handler to both OutputDataReceived and ErrorDataReceived, which fire on separate threads. The handler in GetJavaProperties appends to a shared StringBuilder without synchronization, causing ArgumentException: Destination is too short crashes in CI.

• Add lock around the StringBuilder.AppendLine() call to serialize access to the shared StringBuilder

ProcessUtils.Exec (javaProps, (o, e) => {
    lock (output) {
        output.AppendLine (e.Data);
    }
    // ... rest of handler
});

The lock is scoped to just the StringBuilder since Java outputs property settings to stderr and version info to stdout — the property parsing state (props, curKey, foundPS) is only meaningfully modified by stderr data and doesn't have concurrent writers.

[Copilot]

Pull request overview

Fixes a CI crash in Xamarin.Android.Tools.AndroidSdk JDK property discovery by making JdkInfo.GetJavaProperties() safe when ProcessUtils.Exec() invokes the same DataReceivedEventHandler concurrently from both stdout and stderr threads.

Changes:

• Serialize writes to the shared StringBuilder used for capturing java output by adding a lock around output.AppendLine(e.Data).