[BUILD] Include nostd/string_view which is used severity.h

[ThomsonTan]

Changes

Please provide a brief description of the changes here.

nostd::string_view is used in severity.h, but the header file is not included which then require the user to include it. This PR add "nostd/string_view.h" to include explicitly.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[marcalff]

LGTM

[codecov]

Codecov Report

Merging #2219 (0f51d43) into main (5466c5b) will not change coverage.
The diff coverage is n/a.

❗ Current head 0f51d43 differs from pull request most recent head c0a7feb. Consider uploading reports for the commit c0a7feb to get more accurate results

Additional details and impacted files

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##             main    #2219   +/-   ##
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  Coverage   87.53%   87.53%           
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  Files         169      169           
  Lines        4889     4889           
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  Hits         4279     4279           
  Misses        610      610