feat: 支持 this 语法

crates/oxide_compiler/src/counter.rs

@@ -440,6 +440,10 @@ impl Compiler {
             Expression::ParenthesizedExpression(p) => {
                 self.count_expression(&p.expression, ctx);
             }
+            Expression::ThisExpression(_) => {
+                ctx.alloc_reg();
+                ctx.projected_pc += 1; // LOAD_VAR from reg 254
+            }
             Expression::UpdateExpression(update) => match &update.argument {
                 SimpleAssignmentTarget::AssignmentTargetIdentifier(_) => {
                     ctx.alloc_reg();

crates/oxide_compiler/src/emitter.rs

@@ -1036,6 +1036,11 @@ impl Compiler {
                 ctx.emit(opcode::encode(OpCode::LOAD_VAR, result_reg, 0, 0));
                 Ok(result_reg)
             }
+            Expression::ThisExpression(_) => {
+                let r = ctx.alloc_reg();
+                ctx.emit(opcode::encode(OpCode::LOAD_VAR, r, 254, 0));
+                Ok(r)
+            }
             _ => Err(format!("unsupported expression type: {:?}", expr)),
         }
     }