Remove StringMap::GetOrCreateValue in favor of StringMap::insert

Having two ways to do this doesn't seem terribly helpful and
consistently using the insert version (which we already has) seems like
it'll make the code easier to understand to anyone working with standard
data structures. (I also updated many references to the Entry's
key and value to use first() and second instead of getKey{Data,Length,}
and get/setValue - for similar consistency)

Also removes the GetOrCreateValue functions so there's less surface area
to StringMap to fix/improve/change/accommodate move semantics, etc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222319 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/StringMap.h

@@ -296,7 +296,7 @@ public:
   }
 
   ValueTy &operator[](StringRef Key) {
-    return GetOrCreateValue(Key).getValue();
+    return insert(std::make_pair(Key, ValueTy())).first->second;
   }
 
   /// count - Return 1 if the element is in the map, 0 otherwise.
@@ -363,19 +363,6 @@ public:
     NumTombstones = 0;
   }
 
-  /// GetOrCreateValue - Look up the specified key in the table.  If a value
-  /// exists, return it.  Otherwise, default construct a value, insert it, and
-  /// return.
-  template <typename InitTy>
-  MapEntryTy &GetOrCreateValue(StringRef Key, InitTy &&Val) {
-    return *insert(std::pair<StringRef, ValueTy>(
-                       Key, std::forward<InitTy>(Val))).first;
-  }
-
-  MapEntryTy &GetOrCreateValue(StringRef Key) {
-    return GetOrCreateValue(Key, ValueTy());
-  }
-
   /// remove - Remove the specified key/value pair from the map, but do not
   /// erase it.  This aborts if the key is not in the map.
   void remove(MapEntryTy *KeyValue) {