LibJS/JIT: Update "unwind context" stack in JIT code

Until now, the unwind context stack has not been maintained by jitted
code, which meant we were unable to support the `with` statement.
This is a first step towards supporting that by making jitted code
call out to C++ to update the unwind context stack when entering/leaving
unwind contexts.

We also introduce a new "Catch" bytecode instruction that moves the
current exception into the accumulator. It's always emitted at the start
of a "catch" block.

Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp

@@ -2337,6 +2337,8 @@ Bytecode::CodeGenerationErrorOr<void> TryStatement::generate_bytecode(Bytecode::
         auto& handler_block = generator.make_block();
         generator.switch_to_basic_block(handler_block);
 
+        generator.emit<Bytecode::Op::Catch>();
+
         if (!m_finalizer)
             generator.emit<Bytecode::Op::LeaveUnwindContext>();