[Godot] Add pattern matching and string interpolation to GDScript's page

GDScript supports pattern matching in match statements:

```gdscript
match character:
var p when character is Character: print("Friend!")
var p when character is Enemy: print("Enemy!")
var p when character is NPC: print("Hi, i guess")
_: print("Nothing relevant")
```

But the page doesn't explain that. Also there is typed string interpolation and doesn't is in the page as well:

```gdscript
for i in 100:
print("%d is even?: %s" % [i, i % 2])
```