[mono] Convert Environment.CurrentManagedThreadId to an icall (#20313)

[mono] Convert Environment.CurrentManagedThreadId to an icall (#20313)

In order to avoid the static Thread initialization (System.Thread.CurrentThread inits a static field) see https://github.com/dotnet/runtime/pull/41360

Benchmark:
```csharp
[Benchmark]
public int CurrentThreadId() => Environment.CurrentManagedThreadId;
```

Mono JIT (benchmarked on a slow machine):
```
       |          Method |     Mean |     Error |    StdDev |
       |---------------- |---------:|----------:|----------:|
master | CurrentThreadId | 7.191 ns | 0.0128 ns | 0.0107 ns |
PR     | CurrentThreadId | 5.034 ns | 0.0395 ns | 0.0350 ns |
```

Co-authored-by: EgorBo <EgorBo@users.noreply.github.com>