[BUG] MaskedCategorical missing mode and deterministic_sample properties.

[MorganeAyle]

Describe the bug

Similar issue as here. The MaskedCategorical distribution is missing the mode and deterministic_sample properties.

Reason and Possible fixes

The MaskedCategorical distribution should define the following additional properties:

@property
def mode(self) -> torch.Tensor:
    if hasattr(self, "logits"):
        return self.logits.max(-1, keepdim=True)[1]
    return self.probs.max(-1, keepdim=True)[1]

@property
def deterministic_sample(self) -> torch.Tensor:
    return self.mode