feat: use privacy-preserving webxdc addresses (#6237)

this PR adds the address to be used by the UI for
`window.webxdc.selfAddr` to webxdc-info. UIs need to be changed
accordingly and must not use configured_addr any longer.

the address is created by sha256(private-key + rfc724_mid) , which
results in different addresses for each webxdc, without the option to
find out the real address of the user.

this also returns the same address for a multi-device-setup - sending
totally random self address around might be an alternative, however
would require connectivity (both devices may be offline on first start).

for existing app, after the change, there will be a new user, resulting
eg. in a new highscore, otherwise, things should be mostly fine. this
assumption is also important as we might change the thing another time
when it comes to multi-transport.

ftr, addresses look like
`0f187e3f420748b03e3da76543e9a84ecff822687ce7e94f250c04c7c50398bc` now

when this is merged, we need to adapt #6230 and file issues for all UI
to use `info.selfAddr`

closes #6216

deltachat-rpc-client/tests/test_webxdc.py

@@ -24,6 +24,7 @@ def test_webxdc(acfactory) -> None:
         "name": "Chess Board",
         "sourceCodeUrl": None,
         "summary": None,
+        "selfAddr": webxdc_info["selfAddr"],
     }
 
     status_updates = message.get_webxdc_status_updates()