[JENKINS-59656] check build id before interrupting from the executors widget (#4264)

* [JENKINS-59656] when stopping a Run via the executors widget, make sure it's the intended one

* [JENKINS-59656] added Executor.stopBuild(String) instead of .stop(String)

* revert change to deprecated doStop(StaplerRequest,StaplerResponse), useless now that it's doStopBuild(String) which takes a runExtId parameter

* javadoc: "@since TODO" rather than "@since 2.???"

* [JENKINS-59656] added test case

* jelly cleanup with h.urlEncode(String)

* make Functions.urlEncode(null) return empty String

* Executor.doStopBuild(runExtId): ignore runExtId if executable is not a Run

* Executor.doStopBuild(runExtId) doesn't have to be a public API