tdf#149449 Don't ignore CSS class redefinition inside SVGs

tdf#149449 Don't ignore CSS class redefinition inside SVGs

Previously if a css class was redefined like so:

.cls2,.cls3{fill:#fff;}.cls-2{opacity:0.1;}

the second definition of .cls-2 would get ignored and opacity would
remain 1.

This patch keeps track of the names of each previously defined class and
makes sure to append the future redefinition instead of ignoring it.

Change-Id: I20b55aea247d11774cd743505a90f1466f622b1e
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/136109
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>
(cherry picked from commit 99f8e8aa0ccb741c2b5ede6cab75798c1793d899)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/136244
Reviewed-by: Xisco Fauli <xiscofauli@libreoffice.org>
(cherry picked from commit 34e08a82a317e06d2526f5a16a522323c3902bd7)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/136981