misc: chore: Use explicit types in GPU, Device, and Host1x projects

src/Ryujinx.Graphics.Host1x/Devices.cs

@@ -20,7 +20,7 @@ namespace Ryujinx.Graphics.Host1x
 
         public void Dispose()
         {
-            foreach (var device in _devices.Values)
+            foreach (IDeviceState device in _devices.Values)
             {
                 if (device is ThiDevice thi)
                 {

src/Ryujinx.Graphics.Host1x/Host1xDevice.cs

@@ -46,7 +46,7 @@ namespace Ryujinx.Graphics.Host1x
 
         public void RegisterDevice(ClassId classId, IDeviceState device)
         {
-            var thi = new ThiDevice(classId, device ?? throw new ArgumentNullException(nameof(device)), _syncptIncrMgr);
+            ThiDevice thi = new ThiDevice(classId, device ?? throw new ArgumentNullException(nameof(device)), _syncptIncrMgr);
             _devices.RegisterDevice(classId, thi);
         }