The `#args` and `#gatewayMethod` SpEL variables have been deprecated for a while
* Remove their population and usage in favor of `MethodArgsHolder` `root` of the evaluation context
This change optimize a gateway mapping logic the way that there is no need in evaluation context
for every call: we can just reuse a global one
* Some other `GatewayMethodInboundMessageMapper` code style refactoring
* Fix effected test classes and their configs
a30dc10447