SocketAddress rework

[kjbracey]

Summary of changes

• 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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[kjbracey]

This relates to #12455 - that compiler fault was probably triggered by the complexity of SocketAddress's default construction. (Construct a defaulted temporary nsapi_addr_t, then pass it by value to a constructor).

[ciarmcom]

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

[0xc0170]

Unittest failed (will be reported soon)

Lot of fine fixes here but squashing them into one, makes it hard to fix issues in the future if anything found in this commit.. I would split this one into at least 3 as stated in the Impact of changes (3 points) - they do not look related besides "rework"

[0xc0170]

@ARMmbed/mbed-os-ipcore as @kjbracey-arm is OoO, is there anyone else who could push this forward ?

[kivaisan]

I'll check the UT.

[mbed-ci]

Test run: FAILED

Summary: 1 of 3 test jobs failed
Build number : 1
Build artifacts

Failed test jobs:

• jenkins-ci/mbed-os-ci_unittests

[0xc0170]

Closing to continue in the referenced ^^ PR