Bitwise `&` against `KeyModifierMask` not implemented for `Key`

I wrote the following and got a compiler error:

```rust
let press = x.get_physical_keycode_with_modifiers();
let k = press & KeyModifierMask::CODE_MASK;
```

```
central.rs(659, 5): `Key` does not implement `BitAnd`
```

However, it looks like `BitOr` is implemented.

I'm using `godot = "0.5.5"`.

Start at central.rs around line 659 and inspect the existing BitOr implementation for Key and KeyModifierMask. Add the corresponding BitAnd behavior for the reported expression, then verify that code using KeyModifierMask::CODE_MASK compiles and behaves consistently with BitOr.

Written by the indexing model from the issue text.