[TableGen] Extract InstructionEncoding class into a separate file (NFC)

Author: s-barannikov

llvm/utils/TableGen/Common/CMakeLists.txt

@@ -29,6 +29,7 @@ add_llvm_library(LLVMTableGenCommon STATIC OBJECT EXCLUDE_FROM_ALL DISABLE_LLVM_
   CodeGenTarget.cpp
   DAGISelMatcher.cpp
   InfoByHwMode.cpp
+  InstructionEncoding.cpp
   OptEmitter.cpp
   PredicateExpander.cpp
   SubtargetFeatureInfo.cpp