`SubViewport` children of `SubViewportContainer` don't all receive mouse click input events due to being set to handled

### Tested versions

- Reproducible in: 4.2.2.rc1.official.c7fb0645a

### System information

Ubuntu 22.10, Vulkan, NVIDIA GeForce RTX™ 2060 / NVIDIA GeForce RTX™ 2060

### Issue description

Having a setup like:
```
- SubViewportContainer
- SubViewport1
- SubViewport2
- ...
```
Only one `SubViewport` gets a mouse button pressed event (possibly other mouse events too). Probably because `SubViewportContainer` sets `SubViewport.handle_input_locally` to `false` and because the container itself sets the event as handled.

I tested the setup with an `Area2D._input_event()`. It might have to do with `Viewport.physics_object_picking` being set to `true` so that `Area2D` can interact with the mouse.

### Steps to reproduce

Open the Minimal Reproduction Project. Make sure to turn on *Debug > Vissible Collision Shapes*, run the project, and click on the `Area2D`s. Notice that only one print function is called, but the message should be printed twice.

The hack solution is to force `SubViewport.handle_input_locally` to `true`.

### Minimal reproduction project (MRP)

[godot-dbg.zip](https://github.com/godotengine/godot/files/14468200/godot-dbg.zip)

Run the linked Minimal Reproduction Project with Debug > Visible Collision Shapes enabled and click both Area2Ds. Start at SubViewportContainer, SubViewport.handle_input_locally, and Area2D._input_event(), then verify that each SubViewport child receives its mouse event without relying on the hack that forces local handling.

Written by the indexing model from the issue text.