[dotnet] Improve logging performance when it is disabled

[nvborisenko]

Description

It adds IsEnabled method to check there is handler and event can be emitted. Now internally we should use the following pattern to emit a message:

if (logger.IsEnabled(LogEventLevel.Trace))
{
  logger.Trace("my message");
}

Motivation and Context

Fixes #13411

Benchmark

Code:

[Benchmark]
public void EmitLogOld()
{
    var message = new string('a', 1000);

    logger.Trace(message);
}

[Benchmark]
public void EmitLogNew()
{
    if (logger.IsEnabled(LogEventLevel.Trace))
    {
        var message = new string('a', 1000);

        logger.Trace(message);
    }
}

Results:

| Method     | Mean       | Error     | StdDev    | Gen0   | Allocated |
|----------- |-----------:|----------:|----------:|-------:|----------:|
| EmitLogOld | 213.412 ns | 4.0365 ns | 3.7757 ns | 0.3226 |    2024 B |
| EmitLogNew |   9.917 ns | 0.2251 ns | 0.3369 ns |      - |         - |

I also tried with MethodImpl attribute with aggressive inlining, got mean = 9.1 ns. Decided to not use it, keeping code simple.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.