This commit is about documenting some weird new behavior.

Since Chormium 72 our webChannelWithBadString fails. This is
fascinating issue and can be tracked down to commit in Chromium
https://chromium-review.googlesource.com/c/1282993


which "fixes" well-forming of JSON.strigify. This function
is used by webchannel.js to send data through webchannel
transport. In c++ land we get now for invalid utf16 replacement
in form of '\\u' + i.toString(16).padStart(4, '0').
This sadly does not trigger any longer REPLACE_INVALID_UTF8 in
WebChannelTransport::NativeQtSendMessage. Moreover
this goes even "worse" since QMetaObjectPublisher
will create invalid utf16 form raw "\ud800" string -> '\ud800'.

This is not an error per se, since test creates invalid utf16
character in javascript  and it ends as invalid utf8 character in c++.

Btw enable test on qemu.

Change-Id: I36f2df417d7b9f3f2113792f08025821737d8d01
Reviewed-by: Jüri Valdmann <juri.valdmann@qt.io>