Add target to binding specification: external binding specs #1297
Description
This sub-issue is part of #1232. It concerns processing of the target specified in an external binding specification.
The target of the bindings currently being generated is referred to as the current target.
If an external binding specification specifies a specific target, then it must exactly match the current target. A mismatch should trace an error message.
If an external binding specification specifies target any, it may be used regardless of the current target.