Incorrect casing for extended splashscreen on Wasm

[jeromelaban]

The following line should use the default casing (AppManifest.js):

uno.toolkit.ui/src/Uno.Toolkit.UI/Controls/ExtendedSplashScreen/ExtendedSplashScreen.Windows.crossruntime.cs

Line 38 in 5a6230b

private const string WasmAppManifestFilename = "appmanifest.js";

Related to unoplatform/uno#20607 (reply in thread).

As a workaround, including the AppManifest.js file is an EmbeddedResource can be used.