FilterLogger should respect inner logger's IsEnabled

[andriysavin]

Currently, at https://github.com/aspnet/Logging/blob/dev/src/Microsoft.Extensions.Logging.Filter/Internal/FilterLogger.cs#L27 only provided filter is respected. But this functionality will likely be used for integration with existing logging frameworks, which may have their own filtering system. Why not respect it at least like this:
public bool IsEnabled(LogLevel logLevel) { return _filter(logLevel) && _innerLogger.IsEnabled(logLevel); }

In other words, this filtering decorator should augment inner logger's filtering, not replace it.

[HaoK]

@pakrym was this fixed by your changes?

[pakrym]

Should be fixed, but I haven't verified.

[muratg]

Assigning to @pakrym for investigation.

[pakrym]

Microsoft.Extensions.Logging.Filter is getting removed. New way of adding filters has this fixed.