install,export: Maybe transform OBJECT libraries to INTERFACE libraries

Teach the install and export commands to support installing and exporting OBJECT libraries without their object files. Transform them to INTERFACE libraries in such cases.

For install(TARGETS), activate this when no destination for the object files is specified. For export, activate this only under Xcode with multiple architectures when we have no well-defined object file locations to give to clients.

Do: test

added workflow:in-review label

This merge request has been queued for testing. Test results may be viewed on:

• CDash (master)
• Buildbot (master) (only visible from inside Kitware)

Branch-at-master: ea0ce73a

mentioned in merge request !1524 (merged)

Do: stage

added workflow:nightly-testing and removed workflow:in-review labels

Do: merge

removed workflow:nightly-testing label

mentioned in commit 61f92e69

merged

mentioned in issue #18935