DataflowRunner support for Class-Path jars

See https://github.com/GoogleCloudPlatform/DataflowJavaSDK/issues/538

The code that infers `--filesToStage` from the classpath does not seem to support a classpath jar. which uses a `Class-Path` manifest to indicate which other jars are needed at runtime. This is apparently a standard, approved way to pass the classpath.

We need to add this support to `DataflowRunner#detectClasspathResourcesToStage`, but correctly representing the user's classpath continues to be challenging.

(As `FlinkRunner` has copied this code, we should probably either pull the common utility somewhere public or update the FlinkRunner too?)

Imported from Jira [BEAM-1325](https://issues.apache.org/jira/browse/BEAM-1325). Original Jira may contain additional context.
Reported by: dhalperi.

Start with DataflowRunner#detectClasspathResourcesToStage and review the referenced BEAM-1325 context. Trace how a classpath jar's Class-Path manifest is handled, then compare the copied logic in FlinkRunner. Done means the required jars are correctly represented and staged, with the FlinkRunner/common-utility impact resolved.

Written by the indexing model from the issue text.