VoIP call events are in a bonkers confusing order

[ara4n]

https://spec.matrix.org/unstable/client-server-api/#voice-over-ip

Issue

We list the voip events in alphabetic order:

• m.call.answer
• m.call.candidates
• m.call.hangup
• m.call.invite

Expected behaviour

...whereas it should be a semantically meaningful order:

• invite
• answer
• candidates
• hangup

Pretty sure the order used to be right, so this is a regression.