Remove Iot Core specific topic and client id validation checks in MQTT5

[bretambrose]

• Removes IoT Core specific topic length and segment count validation for subscribe, unsubscribe, and publish
• Removes Iot Core specific client id length validation
• Removes all validation tests checking these properties
• Adds skipping $share/<share-name> to the iot core validation utility functions. Adds testing for the additional functionality.

Leaves the validation utility functions intact. We have determined these were not necessary in MQTT5 (and unnecessary client-side validation should always be avoided for future-compatibility reasons) as IoT Core now returns sensible reason codes that help us diagnose these issues (when using MQTT5; MQTT311 continues to be impacted due to the limitations of the spec). We may revisit and use this functionality as an opt-in setting on the 311 client to help prevent/diagnose particular problems.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Patch coverage: 75.00% and project coverage change: +0.11% 🎉

Comparison is base (b7a323d) 82.12% compared to head (51368c0) 82.24%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #315      +/-   ##
==========================================
+ Coverage   82.12%   82.24%   +0.11%     
==========================================
  Files          20       20              
  Lines        8679     8660      -19     
==========================================
- Hits         7128     7122       -6     
+ Misses       1551     1538      -13     

Files Changed	Coverage Δ
source/v5/mqtt5_utils.c	80.09% <72.41%> (-2.69%)	⬇️
source/v5/mqtt5_options_storage.c	90.59% <100.00%> (+0.09%)	⬆️

... and 3 files with indirect coverage changes

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