Consider rewording warnings around DAM to not mention reflection access

With the following program:

```c#
class Program
{
public static void Main()
{
Foo(typeof(Program));
Bar(typeof(Program));
}

public static void Foo([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties)] Type type)
=> Console.WriteLine("Foo");

public static void Bar([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)] Type type)
=> Console.WriteLine("Bar");
}
```

... the following linker warnings are emitted (dotnet SDK 6.0.101):

```
/home/roji/projects/test/Program.cs(13,9): Trim analysis warning IL2111: Program.Main(): Method 'Program.Foo(Type)' with parameters or return value with `DynamicallyAccessedMembersAttribute` is accessed via reflection. Trimmer can't guarantee availability of the requirements of the method. [/home/roji/projects/test/Test.csproj]
/home/roji/projects/test/Program.cs(13,9): Trim analysis warning IL2111: Program.Main(): Method 'Program.Bar(Type)' with parameters or return value with `DynamicallyAccessedMembersAttribute` is accessed via reflection. Trimmer can't guarantee availability of the requirements of the method. [/home/roji/projects/test/Test.csproj]
```

... although there's no reflection involved.

Curiously, when commenting out the call to Bar, both warnings disappear.