Baseline should include XSLTs

[cambot]

The mapping configuration for CSP files also allows the inclusion of XSLTs. However, the baselining function does not automatically include this file type and it should.

[cambot]

I found this section in the online docs helpful for being able to edit XSLTs from VS Code, but wasn't sure how to include it in this repo's docs.

[isc-pbarton]

Resolved by #816 - thank you @cambot for your contribution