Add basic component composition support

- Handle yield_component statement type
- Call child component render function
- Enables: yield VerticalTabs()
- All tests passing (30/30)
- Tabs.wasm size: 3185 → 3205 bytes

examples/tabs/Tabs.ll

@@ -463,6 +463,7 @@ match.case2.var96:
   %var128 = call i32 @js_create_text(i8* getelementptr inbounds ([55 x i8], [55 x i8]* @.str.61, i32 0, i32 0))
   call void @js_append_child(i32 %var127, i32 %var128)
   call void @js_append_child(i32 %var124, i32 %var127)
+  call void @render_VerticalTabs()
   br label %match.end.var96
 match.case3.var96:
   %var129 = call i32 @js_create_element(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.0, i32 0, i32 0))