Avoid allocating CompositeLogger and related components when disabled

[stevejgordon]

When logging options do not require logging in any form, we should consider using the shared NullLogger instance to avoid allocating the logging infrastructure that is unused. This will require refactoring some internal APIs to prefer ILogger and may not be entirely possible.

This issue should serve as a reminder for an investigation into the impact and whether this is possible.

The allocation overhead is low so this is low priority.