SocketAddress rework

[kivaisan]

Summary of changes

Original work: #12468 . This PR contains also the UT fix.

• Add optimised constexpr default constructor. Default construction was previously by a heavyweight defaulted nsapi_addr_t parameter.
• Remove deprecated resolving constructor.
• Take nsapi_addr_t inputs by constant reference rather than value.
• Inline the trivial getters and setters.
• Use unique_ptr to manage the text buffer.
• Make operator bool explicit.
• Optimise some methods.
• Update to C++11 style (default initialisers, nullptr etc)

Impact of changes

• Constructor deprecated in Mbed OS 5.1 removed.
• Code size reductions, particularly on default initialisation.
• Implicit assignments to bool or int or others no longer possible - any existing code which does not compile is most likely an error. (if (sockaddr) is still fine - such "contextual conversions to bool" can use the explicit operator).

Migration actions required

• Code attempting resolution by passing a hostname to SocketAddress's constructor must be modified to use NetworkInterface::gethostbyname or NetworkStack::gethostbyname.
• Code failing due to the now-explicit bool operator should be reviewed to check intent.

Documentation

n/a

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Pull request type

[] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[X] 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

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[0xc0170]

As previous PR was approved, although I made a comment there about having one commit for this rework is not ideal for future maintenance. @kivaisan Would you be able to split the first commit ?

I started CI meanwhile

[ciarmcom]

@kivaisan, thank you for your changes.
@ARMmbed/mbed-os-tools @ARMmbed/mbed-os-ipcore @ARMmbed/mbed-os-maintainers please review.

[mbed-ci]

Test run: FAILED

Summary: 1 of 6 test jobs failed
Build number : 1
Build artifacts

Failed test jobs:

• jenkins-ci/mbed-os-ci_greentea-test

[0xc0170]

Test failed, but I saw this recently in another PR.

DISCO_L475VG_IOT01A-ARMC6.features-storage-tests-kvstore-direct_access_devicekey_test fails with hard fault. This looks related to minimal printf however it fails there as well (opened PR with a fix)

@ARMmbed/mbed-os-storage Please review, looks like this is on master as well.

[SeppoTakalo]

Same failure as in the minimal-printf PR.
However, as both PRs don't really touch any areas that can affect the test, I suspect HW failure.
Can someone remove that particular board from CI.
Maybe erase-program cycle is now over.

[0xc0170]

Just read your comment there, I notified the test team to check the board.

[0xc0170]

test restarted