gdb: More cleanup changes

- Move the message handler into its debugger class part,
- Move all message types into one file and collapse 3 of the ones with no data into a generic, stateless message with a single property being its type,
- Add an Fpscr helper property on IExecutionContext along with a comment about what Fpscr is (similar to the other registers in there)
- Moved the Rcmd helpers (such as GetRegisters, GetMinidump, etc) into a dedicated Debugger class part,
- Fixed the double-collection (ToArray being called twice) in GetThreadUids & GetThread in KProcess

src/Ryujinx.HLE/Debugger/IMessage.cs

@@ -0,0 +1,47 @@
+using Ryujinx.Cpu;
+
+namespace Ryujinx.HLE.Debugger
+{
+    /// <summary>
+    ///     Marker interface for debugger messages.
+    /// </summary>
+    interface IMessage;
+
+    public enum MessageType
+    {
+        Kill,
+        BreakIn,
+        SendNack
+    }
+
+    record struct StatelessMessage(MessageType Type) : IMessage
+    {
+        public static StatelessMessage Kill => new(MessageType.Kill);
+        public static StatelessMessage BreakIn => new(MessageType.BreakIn);
+        public static StatelessMessage SendNack => new(MessageType.SendNack);
+    }
+
+    struct CommandMessage : IMessage
+    {
+        public readonly string Command;
+
+        public CommandMessage(string cmd)
+        {
+            Command = cmd;
+        }
+    }
+    
+    public class ThreadBreakMessage : IMessage
+    {
+        public IExecutionContext Context { get; }
+        public ulong Address { get; }
+        public int Opcode { get; }
+
+        public ThreadBreakMessage(IExecutionContext context, ulong address, int opcode)
+        {
+            Context = context;
+            Address = address;
+            Opcode = opcode;
+        }
+    }
+}