Added copy constructor

[ahcorde]

Signed-off-by: ahcorde [email protected]

🎉 New feature

Summary

Added Copy constructor to KeyEvent. Required by this PR gazebosim/gz-gui#224

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge

[codecov]

Codecov Report

Merging #224 (2ae2e5f) into ign-common3 (153f320) will increase coverage by 0.03%.
The diff coverage is 94.44%.

❗ Current head 2ae2e5f differs from pull request most recent head 466bbc3. Consider uploading reports for the commit 466bbc3 to get more accurate results

@@               Coverage Diff               @@
##           ign-common3     #224      +/-   ##
===============================================
+ Coverage        76.50%   76.53%   +0.03%     
===============================================
  Files               73       73              
  Lines            10361    10379      +18     
===============================================
+ Hits              7927     7944      +17     
- Misses            2434     2435       +1     

Impacted Files	Coverage Δ
events/src/KeyEvent.cc	98.11% <94.44%> (-1.89%)	⬇️

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