Add support for switch instruction

[vitek-karas]

Find the test to repro this with below (note that simplifying the switches tends to NOT repro it, Roslyn will only use the switch instruction in some cases, for simple switches it tends to use if/else branches).

The problem is that switch instruction is of variable length. In the MethodBodyNode.WriteInternal we "copy" instructions over to the output, relying on Opcode helper to determine the length of the instruction. This doesn't work for switch. The fix is to parse the switch instruction manually and write it out manually as well.

Repro (just add a "Switch.cs" into Basic tests and paste the code below):

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using Mono.Linker.Tests.Cases.Expectations.Assertions;

namespace Mono.Linker.Tests.Cases.Basic
{
    public class Switch
    {
        public static void Main()
        {
            TestSwitchStatement(1);
            TestSwitchExpression(1);
        }

        [Kept]
        public static void TestSwitchStatement(int p)
        {
            switch (p)
            {
                case 0: Case1(); break;
                case 1: Case1(); break;
                case 3: Case1(); break;
                case 4: Case1(); break;
                case 5: Case1(); break;
                case 6: Case1(); break;
                case 7: Case1(); break;
                case 8: Case1(); break;
                case 9: Case1(); break;
                case 10: Case1(); break;
                default:
                    Case2();
                    break;
            }
        }

        [Kept]
        public static void Case1() { }
        [Kept]
        public static void Case2() { }

        [Kept]
        public static int TestSwitchExpression(int p) =>
            p switch
            {
                0 => 1,
                1 => 2,
                2 => 3,
                3 => 4,
                4 => 5,
                5 => 6,
                6 => 7,
                7 => 8,
                8 => 9,
                9 => 10,
                _ => 0
            };
    }
}