Support `ILogger.BeginScope`

[hadashiA]

Add implementation of BeginScope(...) for ILogger.

Note on implementation:

• Add ISupportExternalScope implementation to ILoggerProvider.
  • ILoggerProvider holds IExternalScopeProvider.
  • Also, ILogger (AsyncProcessZLogger) holds the IExternalScopeProvider.
• Add IZLoggerEntry.ScopeState property. It enables scope information to be retained.
  • The logger uses IExternalScopeProvider.ForeEachScope to create a copy of the value when creating a log entry.
  • Handles scope information as IEnumerable<KeyValuePair<string, object?>>.