perf: set capacity of List in MembersForcedLine (#1709)

Most `result` Lists are always just under `3 * members.Count`, small
change but simple 🤷


### Benchmarks (timing is inaccurate should be the same)
#### Before
| Method | Mean | Error | StdDev | Gen0 | Gen1 | Allocated |
|------------------------------
|---------:|--------:|--------:|----------:|----------:|----------:|
| Default_CodeFormatter_Tests | 133.0 ms | 2.56 ms | 2.84 ms | 3000.0000
| 1000.0000 | 34.58 MB |
| Default_CodeFormatter_Complex | 271.5 ms | 5.40 ms | 7.92 ms |
5000.0000 | 2000.0000 | 52.95 MB |


#### After
| Method | Mean | Error | StdDev | Gen0 | Gen1 | Allocated |
|------------------------------
|---------:|--------:|--------:|----------:|----------:|----------:|
| Default_CodeFormatter_Tests | 132.4 ms | 2.64 ms | 3.87 ms | 3000.0000
| 1000.0000 | 34.56 MB |
| Default_CodeFormatter_Complex | 268.2 ms | 4.92 ms | 4.60 ms |
5000.0000 | 2000.0000 | 52.78 MB |

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

Author: TimothyMakkison

Src/CSharpier.Core/CSharp/SyntaxPrinter/MembersWithForcedLines.cs

@@ -20,7 +20,7 @@ public static List<Doc> Print<T>(
     )
         where T : MemberDeclarationSyntax
     {
-        var result = new List<Doc>();
+        var result = new List<Doc>(members.Count * 3);
         if (!skipFirstHardLine)
         {
             result.Add(Doc.HardLine);