LibJS/Bytecode: Implement the delete unary expression

`delete` has to operate directly on Reference Records, so this
introduces a new set of operations called DeleteByValue, DeleteVariable
and DeleteById. They operate similarly to their Get counterparts,
except they end in creating a (temporary) Reference and calling delete_
on it.

Userland/Libraries/LibJS/Bytecode/Instruction.h

@@ -23,6 +23,9 @@
     O(CreateEnvironment)             \
     O(CreateVariable)                \
     O(Decrement)                     \
+    O(DeleteById)                    \
+    O(DeleteByValue)                 \
+    O(DeleteVariable)                \
     O(Div)                           \
     O(EnterUnwindContext)            \
     O(EnterObjectEnvironment)        \