Make commons-lang3 optional

[basil]

Jenkins core ships commons-compress (where it is available to all Jenkins plugins) for historical reasons, but not commons-lang3. Instead we prefer to deliver commons-lang3 through the Jenkins plugin system. commons-compress has recently sprouted a dependency on commons-lang3, which has forced us to start delivering commons-lang3 in core, which we don't want to do. This library is only used in org.apache.commons.compress.harmony.unpack200.Pack200UnpackerAdapter which we don't use anyway, so make this an optional dependency. People who use Pack200UnpackerAdapter can include it, but those of us who would rather avoid it can do without.

[garydgregory]

-1: We are moving away from using Maven optional dependencies. If you know that a code path will never hit a dependency, you can exclude it I suppose.

[basil]

I have done that in jenkinsci/jenkins#8997. Maybe you can find a way to do without FieldUtils in src/main and then convert it to a test-scoped dependency.

[garydgregory]

Closing: Information provided; see #490 for a possible alternate path.