UserspaceEmulator+LibX86: Clean up some obnoxious template spam

Don't require clients to templatize modrm().read{8,16,32,64}() with
the ValueWithShadow type when we can figure it out automatically.
The main complication here is that ValueWithShadow is a UE concept
while the MemoryOrRegisterReference inlines exist at the lower LibX86
layer and so doesn't have direct access to those types. But that's
nothing we can't solve with some simple template trickery. :^)

DevTools/UserspaceEmulator/SoftCPU.h

@@ -53,6 +53,11 @@ class SoftCPU final
     : public X86::Interpreter
     , public X86::InstructionStream {
 public:
+    using ValueWithShadowType8 = ValueWithShadow<u8>;
+    using ValueWithShadowType16 = ValueWithShadow<u16>;
+    using ValueWithShadowType32 = ValueWithShadow<u32>;
+    using ValueWithShadowType64 = ValueWithShadow<u64>;
+
     explicit SoftCPU(Emulator&);
     void dump() const;