ensure to-device verification is compatible between riot web, riotx and riot ios

[bwindels]

riot-web currently expects a .request event to start a verification request, even for to_device requests. It's possible riot ios and riotx are still initiating these with a .start request. There was talk in #12320 is simplying the spec but that hasn't seen any follow up. Whatever we do, we obviously need it to work between riot on all platforms

Ensure that:

• riot ios can receive to_device requests from riot-web
• riot web can receive to_device requests from riot-ios
• riotx can receive to_device requests from riot-web
• riot web can receive to_device requests from riotx
• the spec reflects what is implemented in all riots

[bwindels]

riotx should work according to valere, still good to test probably.

[bwindels]

valere says:
self verification is .request
verify user is .request
And if you open device list of a user ,that has not cross signing or/and have untrusted device, you will then have the option to manually verify the device i.e .start