writing to `POSITION` gives wrong `VIEW` in fragment shader

### Tested versions

stable 4.3

### System information

Kubuntu 22.04

### Issue description

If you write to `POSITION` to make a full screen post processor, then your `VIEW` vector will become invalid and you have to calculate it manually.
What i observe that if i write to `POSITION` then the `VIEW` variable will become affected by camera translation.

### Steps to reproduce

write to POSITION

### Minimal reproduction project (MRP)

[viewbugreport.zip](https://github.com/user-attachments/files/17450091/viewbugreport.zip)

Start by opening the attached viewbugreport.zip in Godot 4.3 and reproducing the fragment-shader case that writes to POSITION. Compare VIEW with and without that write while checking the rendering and shader paths involved; done means VIEW remains valid and unaffected by camera translation.

Written by the indexing model from the issue text.