[flang]Add examples in documentation/BijectiveInternalNameUniquing.md

    Summary:
    I thought it would be simpler to understand on how the unique names would
    look like when an example is present. So I added some examples.

    I found 2 such places to add examples
    -Common blocks
    -Module scope global data

    Reviewers: schweitz, kiranchandramohan, sscalpone, jeanPerier, jdoerfert, DavidTruby

    Reviewed By: schweitz, jeanPerier

    Subscribers: llvm-commits, flang-commits

    Tags: #flang, #llvm

    Differential Revision: https://reviews.llvm.org/D79442