Spark fails to launch executors with very large user classpath lists on YARN

When running Spark on YARN, the user-class-path argument to CoarseGrainedExecutorBackend is used to pass a list of user JAR URIs to executor processes. The argument is specified once for each JAR, and the URIs are fully-qualified, so the paths can be quite long. With large user JAR lists (say 1000+), this can result in system-level argument length limits being exceeded, typically manifesting as the error message:

/bin/bash: Argument list too long

A Google search indicates that this is not a theoretical problem and afflicts real users, including ours. This issue was originally observed on Spark 2.3, but has been confirmed to exist in the master branch as well.