LibJS: Rename Environment Records so they match the spec :^)

This patch makes the following name changes:

- ScopeObject => EnvironmentRecord
- LexicalEnvironment => DeclarativeEnvironmentRecord
- WithScope => ObjectEnvironmentRecord

Userland/Libraries/LibJS/Forward.h

@@ -131,7 +131,7 @@ class HandleImpl;
 class Heap;
 class HeapBlock;
 class Interpreter;
-class LexicalEnvironment;
+class DeclarativeEnvironmentRecord;
 class MarkedValueList;
 class NativeFunction;
 class NativeProperty;
@@ -142,7 +142,7 @@ class PromiseResolveThenableJob;
 class PropertyName;
 class Reference;
 class ScopeNode;
-class ScopeObject;
+class EnvironmentRecord;
 class Shape;
 class Statement;
 class StringOrSymbol;