[llvm/Object] - Make ELFObjectFile::getRelocatedSection return Expected<section_iterator>

It returns just a section_iterator currently and have a report_fatal_error call inside.
This change adds a way to return errors and handle them on caller sides.

The patch also changes/improves current users and adds test cases.

Differential revision: https://reviews.llvm.org/D69167

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@375408 91177308-0d34-0410-b5e6-96231b3b80d8
14 files changed