HasConversion<string>() always returns "False"

## File a bug

Here's [the docs section](https://docs.microsoft.com/en-us/ef/core/modeling/value-conversions?tabs=data-annotations#built-in-converters) that details the conversion options (`bool` is at the top).

### Include your code

Model:

```c#
public class MyModel
{
public bool IsTrue { get; set; }
}
```

Context:

```c#
modelBuilder
.Entity(eb =>
{
eb.HasNoKey();
eb.ToView("MyView");
eb.Property(v => v.IsTrue).HasColumnName("yes_no_value").HasConversion(); // this line always returns False
});
```

Changing the mapping/conversion line to the following works:

```c#
eb.Property(v => v.IsTrue).HasColumnName("yes_no_value").HasConversion(new BoolToStringConverter("N", "Y"));
```

### Include provider and version information

EF Core version: 5.0.8
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework: .NET 5.0
Operating system: macOS 11.4
IDE: Visual Studio for Mac 8.10 build 10