Clean up Title packets and enforce action types (fixes #1802)

[WouterGritter]

Closes #1802, this PR builds on-top of the fix proposed and explained in that PR.

This PR drops the method visibility, enforces the action types (similar pattern to the already-existing enforcement in TitleClearPacket) and cleans up some whitespace formatting.

After the third commit, this PR now does away with the setAction() method completely, which was only used within this package. It does not make sense to set the action type at all here; they must be exactly one action for most modern packets, except for TitleClearPacket which supports two types (which is still enforced), and except for LegacyTitlePacket which can still hold any action type.

[WouterGritter]

HeaderAndFooterPacket has a similar situation, where it's never expected to be decoded:

public HeaderAndFooterPacket() {
  throw new UnsupportedOperationException("Decode is not implemented");
}

@Override
public void decode(ByteBuf buf, ProtocolUtils.Direction direction, ProtocolVersion version) {
  throw new UnsupportedOperationException("Decode is not implemented");
}

I'll update this PR to match this convention.