Convert test file to UTF-8

We tell MSVC that our source is UTF-8, but this file really is Latin-9. Chaos ensues.

Convert the file to UTF-8 using 'iconv -f ISO_8859-15 -t UTF-8 termgeneratortest.cpp' and adjust the code accordingly.

This fixes the build with MSVC.

(cherry picked from commit 24141590)
1 job for release/21.12 in 10 minutes and 54 seconds (queued for 347 minutes and 46 seconds)