Reorganize backpatching a bit. Untested on ARM.

Rather than *MemTools.cpp checking whether the address is in the
emulated range itself (which, as of the next commit, doesn't cover every
kind of access the JIT might want to intercept) and doing PC
replacement, they just pass the access address and context to
jit->HandleFault, which does the rest itself.

Because SContext is now in JitInterface, I wanted JitBackpatch.h (which
defines it) to be lightweight, so I moved TrampolineCache and associated
x64{Analyzer,Emitter} dependencies into its own file.  I hate adding new
files in three places, two of which are MSVC...

While I'm at it, edit a misleading comment.

Source/Core/Core/Core.vcxproj

@@ -229,6 +229,7 @@
     <ClCompile Include="PowerPC\JitCommon\JitBase.cpp" />
     <ClCompile Include="PowerPC\JitCommon\JitCache.cpp" />
     <ClCompile Include="PowerPC\JitCommon\Jit_Util.cpp" />
+    <ClCompile Include="PowerPC\JitCommon\TrampolineCache.cpp" />
     <ClCompile Include="PowerPC\JitInterface.cpp" />
     <ClCompile Include="PowerPC\PowerPC.cpp" />
     <ClCompile Include="PowerPC\PPCAnalyst.cpp" />
@@ -406,6 +407,7 @@
     <ClInclude Include="PowerPC\JitCommon\JitBase.h" />
     <ClInclude Include="PowerPC\JitCommon\JitCache.h" />
     <ClInclude Include="PowerPC\JitCommon\Jit_Util.h" />
+    <ClInclude Include="PowerPC\JitCommon\TrampolineCache.h" />
     <ClInclude Include="PowerPC\JitInterface.h" />
     <ClInclude Include="PowerPC\PowerPC.h" />
     <ClInclude Include="PowerPC\PPCAnalyst.h" />
@@ -464,4 +466,4 @@
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">
   </ImportGroup>
-</Project>
+</Project>