Fix BufferedSerial visibility of private base class enum enumerators

[hugueskamba]

Summary of changes

Each enum enumerator needs to be exposed to be usable in the sub class.

Impact of changes

Migration actions required

Documentation

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Pull request type

[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[X] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

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Reviewers

@evedon @kjbracey-arm @0xc0170

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[ciarmcom]

@hugueskamba, thank you for your changes.
@0xc0170 @kjbracey-arm @evedon @ARMmbed/mbed-os-core @ARMmbed/mbed-os-maintainers please review.

[0xc0170]

I was checking this while ago, I did not understand the previous comment about C++1x and not needed using there. @kjbracey-arm Please review

[kjbracey]

I was checking this while ago, I did not understand the previous comment about C++1x and not needed using there. @kjbracey-arm Please review

It seems I was wrong when I wrote that comment in the original code. Something had led me to believe that using a plain enum also gave you its values in C++11, but I can now find no reference to that, nor can I figure out what I might have misinterpreted.

Maybe it was something to do with C++11 enum classes - they would naturally give you Parity::Even if you did using SerialBase::Parity.

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 11 of 11 test jobs passed
Build number : 1
Build artifacts

[adbridge]

@hugueskamba @0xc0170 is this exposing new API parts ? In which case it should be feature update?