After commit 2ab9be54fb we had to rename
the generated CSS files to be included into the GResource bundle; we
kept the URI stable to avoid too much churn, and allow backporting the
change to the 3.24 stable branch. This had the adverse effect of making
it harder to debug issues, as the on-disk file name does not match the
location in the GResource that will be used to print out warnings,
errors, and debugging messages.
Renaming the files from -dark to -inverse makes it more obvious
that this is not a dark variant in the sense of the 'prefer-dark'
setting, but rather a separate theme (sharing the same CSS).
