PowerPC: Remove separate macros for paired singles

Previously, PowerPC.h had four macros in it like so:

\#define rPS0(i) (*(double*)(&PowerPC::ppcState.ps[i][0]))
\#define rPS1(i) (*(double*)(&PowerPC::ppcState.ps[i][1]))

\#define riPS0(i) (*(u64*)(&PowerPC::ppcState.ps[i][0]))
\#define riPS1(i) (*(u64*)(&PowerPC::ppcState.ps[i][1]))

Casting between object representations like this is undefined behavior.
Given this is used heavily with the interpreter (that is, the most
accurate, but slowest CPU backend), we don't exactly want to allow
undefined behavior to creep into it.

Instead, this adds a helper struct for operating with the paired singles,
and replaces the four macros with a single macro for accessing the
paired-singles/floating-point registers.

This way, it's left up to the caller to explicitly decide how it wants to interpret
the data (and makes it more obvious where different interpretations of
the same data are occurring at, as there'll be a call to one of the
[x]AsDouble() functions).

Source/Core/Core/GeckoCode.cpp

@@ -272,8 +272,8 @@ void RunCodeHandler()
   // Registers FPR0->13 are volatile
   for (int i = 0; i < 14; ++i)
   {
-    PowerPC::HostWrite_U64(riPS0(i), SP + 24 + 2 * i * sizeof(u64));
-    PowerPC::HostWrite_U64(riPS1(i), SP + 24 + (2 * i + 1) * sizeof(u64));
+    PowerPC::HostWrite_U64(rPS(i).PS0AsIntegral(), SP + 24 + 2 * i * sizeof(u64));
+    PowerPC::HostWrite_U64(rPS(i).PS1AsIntegral(), SP + 24 + (2 * i + 1) * sizeof(u64));
   }
   DEBUG_LOG(ACTIONREPLAY,
             "GeckoCodes: Initiating phantom branch-and-link. "

Source/Core/Core/HLE/HLE_Misc.cpp

@@ -64,8 +64,8 @@ void GeckoReturnTrampoline()
   PowerPC::ExpandCR(PowerPC::HostRead_U32(SP + 20));
   for (int i = 0; i < 14; ++i)
   {
-    riPS0(i) = PowerPC::HostRead_U64(SP + 24 + 2 * i * sizeof(u64));
-    riPS1(i) = PowerPC::HostRead_U64(SP + 24 + (2 * i + 1) * sizeof(u64));
+    rPS(i).SetBoth(PowerPC::HostRead_U64(SP + 24 + 2 * i * sizeof(u64)),
+                   PowerPC::HostRead_U64(SP + 24 + (2 * i + 1) * sizeof(u64)));
   }
 }
 }

Source/Core/Core/HLE/HLE_VarArgs.cpp

@@ -15,7 +15,7 @@ u32 HLE::SystemVABI::VAList::GetGPR(u32 gpr) const
 
 double HLE::SystemVABI::VAList::GetFPR(u32 fpr) const
 {
-  return rPS0(fpr);
+  return rPS(fpr).PS0AsDouble();
 }
 
 HLE::SystemVABI::VAListStruct::VAListStruct(u32 address)

Source/Core/Core/PowerPC/Interpreter/Interpreter.cpp

@@ -88,8 +88,10 @@ static void Trace(UGeckoInstruction& inst)
   std::string fregs = "";
   for (int i = 0; i < 32; i++)
   {
-    fregs += StringFromFormat("f%02d: %08" PRIx64 " %08" PRIx64 " ", i, PowerPC::ppcState.ps[i][0],
-                              PowerPC::ppcState.ps[i][1]);
+    const auto& ps = PowerPC::ppcState.ps[i];
+
+    fregs += StringFromFormat("f%02d: %08" PRIx64 " %08" PRIx64 " ", i, ps.PS0AsIntegral(),
+                              ps.PS1AsIntegral());
   }
 
   const std::string ppc_inst = Common::GekkoDisassembler::Disassemble(inst.hex, PC);