Frontend: Split blocks at jump target boundaries

With the prior approach, backwards jumps into existing blocks would
explore the overlapping part rather than splitting the block, generating
needless code and wasting time decoding. Similarly, the current block
wouldn't be split when it is extended to overlap with a pending jump target.

Solve this by tracking blocks in a sorted vector and splitting existing blocks
on jumps when appropriate, in order to avoid any possibility of overlapping
blocks, which would break the lookup, misaligned and zero instruction blocks
are disallowed.

FEXCore/Source/Interface/Core/Frontend.h

@@ -22,6 +22,7 @@ public:
   // New Frontend decoding
   struct DecodedBlocks final {
     uint64_t Entry {};
+    uint64_t Size {};
     uint64_t NumInstructions {};
     FEXCore::X86Tables::DecodedInst* DecodedInstructions;
     bool HasInvalidInstruction {};
@@ -70,7 +71,9 @@ private:
   bool DecodeInstruction(uint64_t PC);
 
   void BranchTargetInMultiblockRange();
-  bool BranchTargetCanContinue(bool FinalInstruction) const;
+  bool InstCanContinue() const;
+
+  void AddBranchTarget(uint64_t Target);
 
   uint8_t ReadByte();
   uint8_t PeekByte(uint8_t Offset) const;
@@ -102,11 +105,12 @@ private:
   uint64_t SymbolMaxAddress {};
   uint64_t SymbolMinAddress {~0ULL};
   uint64_t SectionMaxAddress {~0ULL};
+  uint64_t NextBlockStartAddress {~0ULL};
 
   DecodedBlockInformation BlockInfo;
   fextl::set<uint64_t> CurrentBlockTargets;
   fextl::set<uint64_t> BlocksToDecode;
-  fextl::set<uint64_t> HasBlocks;
+  fextl::set<uint64_t> VisitedBlocks;
   fextl::set<uint64_t>* ExternalBranches {nullptr};
 
   // ModRM rm decoding