Add Turkish translation for file associations

[KerimDemirkaynak]

Added Turkish resource strings to src/res/strings_utf8.rc for Windows shell integration.

[KerimDemirkaynak]

Note regarding the CI failure:

The Windows CI build is failing at fragment_setupbase.iss with the following error:
Couldn't open include file "...\ChineseSimplified.isl": The system cannot find the file specified.

This failure is unrelated to my commit. My changes only add the Turkish translation to strings_utf8.rc.

The issue is caused by a very recent upstream change in the Inno Setup repository. As of a few hours ago (June 23), the ChineseSimplified.isl and ChineseTraditional.isl files were moved from the Unofficial directory to their official Languages directory.

Because the Aegisub Windows installer setup script (win-installer-setup.ps1) fetches these files directly using raw GitHub URLs pointing to the old Unofficial path, those downloads are now failing. The CI continues running but fails later at fragment_setupbase.iss because the .isl files were never successfully downloaded.

The PowerShell installer setup script will need to be updated to reflect these new upstream URL paths, but I kept my PR strictly focused on the translation addition.