ComboBoxSlow test upgrade (#14292)

Change-Id: Ic2e1bfd300a6b18aeddd4c4895c7bb11fec5bb8b
TableColumnResizeContentsWidth test upgrade (#14292)

Change-Id: I1adc4dfea7bf62191a23a89440eeca677f47e6a6
ComboBoxValueInput test upgrade (#14292)

Change-Id: Id2158d0990f12940f2206095b8edc0946977f27d
fixes incorrect JSONArray/String usage in ServerRpcHandler (#14471)

As described by Johannes, the RPCRequest constructor first takes whole
JSON as string and builds its attribute json from it (by parsing).
Then it reads from this parsed JSON the array called "rpc".
However it previously did a .toString on it only to re-parse it.
Newer json versions complain that "rpc" is not a string, but an array.

Change-Id: If4bb45abad551b183d757f0aa326c37c070ce103
Merge remote-tracking branch 'origin/master' into 7.3