Rewrite Python TestRail-to-XRay filter in XSLT

[vnaipaul]

Partial contribution towards #14 .

This new XSLT implementation (using XSLT v3; I wasn't able to achieve output parity using XSLT v1 features alone) of the TestRail-to-Xray (cloud) transform produces the same output as its Python original, given the preexisting sample input, comic_estore.xml:

bash-3.2$ pwd
/Users/vnaipaul/git/xray/xray-code-snippets/use_cases/import_from_testrail/cloud
bash-3.2$ git log --oneline main..@
175941a (HEAD -> testrail_xslt, origin/testrail_xslt) Rewrite Python TestRail-to-XRay filter in XSLT
bash-3.2$ python3 testrail2Xray.py -i comic_estore.xml -o comicEstore-by-python.csv
bash-3.2$ xslt3 -xsl:testrail2Xray.xsl -s:comic_estore.xml -o:comicEstore-by-xslt.csv
bash-3.2$ cksum comicEstore-by-*.csv
1070152101 1738 comicEstore-by-python.csv
1070152101 1738 comicEstore-by-xslt.csv