feat: convert PrintCommand to value type (#1505)

Converts `PrintCommand` to a struct, this is a massive memory and
performance improvement 😄
Converting types to a struct sometimes causes regressions from copying
so I had held of on this one.

#### Before
| Method | Mean | Error | StdDev | Gen0 | Gen1 | Gen2 | Allocated |
|----------------------
|---------:|--------:|---------:|----------:|----------:|----------:|----------:|
| Default_CodeFormatter | 206.3 ms | 4.11 ms | 10.00 ms | 7000.0000 |
3000.0000 | 1000.0000 | 66.17 MB |

#### After
| Method | Mean | Error | StdDev | Gen0 | Gen1 | Allocated |
|----------------------
|---------:|--------:|--------:|----------:|----------:|----------:|
| Default_CodeFormatter | 176.3 ms | 3.46 ms | 5.17 ms | 4000.0000 |
2000.0000 | 46.53 MB |


### Using `readonly struct`
I did experiment with making this a `readonly struct` and passing via
`in` see #1506. I'm not convinced this makes an impact although the
difference is likely too small to accurately benchmark.

I opted to benchmark each with the below code. The results appear to
show that a basic struct is faster although this could just be random
noise. Looking at the IL code or profiling with dotTrace might give us
the right answer, for now, I'm happy to settle with the current
solution.
```C#
for (int i = 0; i < 10; i++)
{
    CSharpFormatter
        .FormatAsync(this.largeCode, new PrinterOptions())
        .GetAwaiter()
        .GetResult();
}
``` 


#### 10X Struct
| Method | Mean | Error | StdDev | Gen0 | Gen1 | Gen2 | Allocated |
|----------------------
|--------:|---------:|---------:|-----------:|-----------:|----------:|----------:|
| Default_CodeFormatter | 1.962 s | 0.0307 s | 0.0257 s | 53000.0000 |
29000.0000 | 7000.0000 | 464.31 MB |

| Method | Mean | Error | StdDev | Gen0 | Gen1 | Gen2 | Allocated |
|----------------------
|--------:|---------:|---------:|-----------:|-----------:|----------:|----------:|
| Default_CodeFormatter | 1.980 s | 0.0211 s | 0.0176 s | 53000.0000 |
28000.0000 | 7000.0000 | 464.14 MB |

| Method | Mean | Error | StdDev | Gen0 | Gen1 | Gen2 | Allocated |
|----------------------
|--------:|---------:|---------:|-----------:|-----------:|----------:|----------:|
| Default_CodeFormatter | 1.965 s | 0.0160 s | 0.0142 s | 53000.0000 |
28000.0000 | 7000.0000 | 464.14 MB |

| Method | Mean | Error | StdDev | Gen0 | Gen1 | Gen2 | Allocated |
|----------------------
|--------:|---------:|---------:|-----------:|-----------:|----------:|----------:|
| Default_CodeFormatter | 1.957 s | 0.0164 s | 0.0128 s | 53000.0000 |
28000.0000 | 7000.0000 | 464.14 MB |

#### 10X Readonly Struct
| Method | Mean | Error | StdDev | Gen0 | Gen1 | Gen2 | Allocated |
|----------------------
|--------:|---------:|---------:|-----------:|-----------:|----------:|----------:|
| Default_CodeFormatter | 1.979 s | 0.0249 s | 0.0220 s | 53000.0000 |
28000.0000 | 7000.0000 | 464.14 MB |

| Method | Mean | Error | StdDev | Gen0 | Gen1 | Gen2 | Allocated |
|----------------------
|--------:|---------:|---------:|-----------:|-----------:|----------:|----------:|
| Default_CodeFormatter | 1.971 s | 0.0137 s | 0.0114 s | 53000.0000 |
29000.0000 | 7000.0000 | 464.3 MB |

| Method | Mean | Error | StdDev | Gen0 | Gen1 | Gen2 | Allocated |
|----------------------
|--------:|---------:|---------:|-----------:|-----------:|----------:|----------:|
| Default_CodeFormatter | 1.980 s | 0.0276 s | 0.0245 s | 53000.0000 |
29000.0000 | 7000.0000 | 464.31 MB |

| Method | Mean | Error | StdDev | Gen0 | Gen1 | Gen2 | Allocated |
|----------------------
|--------:|---------:|---------:|-----------:|-----------:|----------:|----------:|
| Default_CodeFormatter | 1.953 s | 0.0139 s | 0.0108 s | 53000.0000 |
28000.0000 | 7000.0000 | 464.14 MB |

Co-authored-by: Bela VanderVoort <[email protected]>

Src/CSharpier/DocPrinter/DocPrinter.cs

@@ -405,7 +405,7 @@ private void Push(Doc doc, PrintMode printMode, Indent indent)
     }
 }
 
-internal record PrintCommand(Indent Indent, PrintMode Mode, Doc Doc);
+internal record struct PrintCommand(Indent Indent, PrintMode Mode, Doc Doc);
 
 internal enum PrintMode
 {