Fix startup crash when publishing game in SingleFile and Portable mode
Fix startup crash when publishing game in SingleFile and Portable mode

Creating a gamehost in portable mode will use the startup path of the
executable as the storage basepath. This basepath is resolved in
`DebugUtils` via `Assembly.GetEntryAssembly()`. When publishing in
SingleFile mode `Assembly.GetEntryAssembly()` will always return an
empty string which causes a crash on startup.

It is recommended to use `AppContext.BaseDirectory` instead.

See: https://docs.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/il3000

ppy/osu-framework,peppy/osu-framework,smoogipooo/osu-framework,ZLima12/osu-framework,peppy/osu-framework,peppy/osu-framework,ZLima12/osu-framework,smoogipooo/osu-framework,ppy/osu-framework,ppy/osu-framework