Change nameFilter of saveDialog from "World files" to "SDF files"

[ijnek]

🦟 Bug fix

Summary

In the world save dialog, the file extension does not show up. By having "World files", many people may misinterpret this to be a .world file (like I did).

By having SDF files, this would at least suggest usage of .sdf file. Without the correct extension, the OK button stays greyed out:

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• 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 and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #1774 (cf10d76) into gz-sim7 (6a8594b) will increase coverage by 0.06%.
The diff coverage is 72.11%.

@@             Coverage Diff             @@
##           gz-sim7    #1774      +/-   ##
===========================================
+ Coverage    64.16%   64.22%   +0.06%     
===========================================
  Files          335      336       +1     
  Lines        26508    26600      +92     
===========================================
+ Hits         17008    17083      +75     
- Misses        9500     9517      +17     

Impacted Files	Coverage Δ
src/SystemLoader.cc	59.50% <44.44%> (+1.54%)	⬆️
src/systems/acoustic_comms/AcousticComms.cc	93.22% <93.22%> (ø)
src/Util.cc	93.39% <0.00%> (-0.32%)	⬇️

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[azeey]

Thanks! Now that we don't use .world files, I think it makes sense to say "SDF files".

[ijnek]

Not sure if CI failure is related.