Rename the HighContastInverse css files

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).

gtk/Makefile.am

@@ -1214,9 +1214,9 @@ gtk.gresource.xml: Makefile.am inspector/Makefile.inc
           echo "    <file preprocess='to-pixdata'>theme/Adwaita/assets/$$n</file>" >> $@; \
         done; \
 	echo "    <file alias='theme/HighContrast.css'>theme/HighContrast/gtk.css</file>" >> $@; \
-	echo "    <file alias='theme/HighContrastInverse.css'>theme/HighContrast/gtk-dark.css</file>" >> $@; \
+	echo "    <file alias='theme/HighContrastInverse.css'>theme/HighContrast/gtk-inverse.css</file>" >> $@; \
 	echo "    <file>theme/HighContrast/gtk-contained.css</file>" >> $@; \
-	echo "    <file>theme/HighContrast/gtk-contained-dark.css</file>" >> $@; \
+	echo "    <file>theme/HighContrast/gtk-contained-inverse.css</file>" >> $@; \
 	if test "$(win32_theme)" = "yes"; then \
 	  for f in $(srcdir)/theme/win32/*.css; do \
 	    n=`basename $$f`; \