LibJS: Stop using execute_ast_node() for class property evaluation

Instead, generate bytecode to execute their AST nodes and save the
resulting operands inside the NewClass instruction.

Moving property expression evaluation to happen before NewClass
execution also moves along creation of new private environment and
its population with private members (private members should be visible
during property evaluation).

Before:
- NewClass

After:
- CreatePrivateEnvironment
- AddPrivateName
- ...
- AddPrivateName
- NewClass
- LeavePrivateEnvironment

Userland/Libraries/LibJS/Bytecode/Instruction.h

@@ -15,6 +15,7 @@
 
 #define ENUMERATE_BYTECODE_OPS(O)      \
     O(Add)                             \
+    O(AddPrivateName)                  \
     O(ArrayAppend)                     \
     O(AsyncIteratorClose)              \
     O(Await)                           \
@@ -31,6 +32,7 @@
     O(CopyObjectExcludingProperties)   \
     O(CreateLexicalEnvironment)        \
     O(CreateVariableEnvironment)       \
+    O(CreatePrivateEnvironment)        \
     O(CreateVariable)                  \
     O(CreateRestParams)                \
     O(CreateArguments)                 \
@@ -88,6 +90,7 @@
     O(JumpUndefined)                   \
     O(LeaveFinally)                    \
     O(LeaveLexicalEnvironment)         \
+    O(LeavePrivateEnvironment)         \
     O(LeaveUnwindContext)              \
     O(LeftShift)                       \
     O(LessThan)                        \