Extend support for partial CPU state reads/writes

This patch implements `VariableManager::storeToCPUStateOffset` and
`VariableManager::loadFromCPUStateOffset`, which handle in a single
point all the accesses by offset to the CPU state.

* `getTypeAtOffset`: introduce a feature to easily debug how we compute
  which field is at a specified offset in the CPU state (`--debug
  type-at-offset`).
* Let `getTypeAtOffset` and its wrappers return the offset inside a
  field of the CPU state (useful when accessing the third byte of an
  integer).
* Use a dedicated class for the `CorrectCPUStateUsage` worklist

codegenerator.cpp

@@ -637,7 +637,8 @@ void CodeGenerator::translate(uint64_t VirtualAddress,
 
   // Instantiate helpers
   VariableManager Variables(*TheModule,
-                            *HelpersModule);
+                            *HelpersModule,
+                            TargetArchitecture);
 
   auto *PCReg = Variables.getByEnvOffset(ptc.pc, "pc").first;
   JumpTargetManager JumpTargets(MainFunction,