The context property version is slower to access and won't be supported
in Qt6. Let's port away from it and use the singleton version instead.
Here was my full process for making this change:
1. Made the change with `find . -name '*.qml' | xargs perl -pi -e 's/units\./PlasmaCore\.Units\./g'`
2. Verified no more occurrences with `grep -r " units."`
3. Made sure this didn't change any comments in a silly way by inspecting the output of `git diff | grep "+ " | grep "//"`
4. Manually inspected the full git diff to make sure there were no other unintentional or silly changes (there were none)
5. verified that all changed files have the PlasmaCore import with the correct name with `for FILE in `git status | grep modified | cut -d ":" -f 3`; do grep -q "as PlasmaCore" $FILE || echo "$FILE needs the PlasmaCore import"; done` (one needed the import)
Since some time PlasmaCore had the very useful ColorScope class,
which can semi-automatically make children take colors of the
View, Button or Complementary color groups.
Unfortunately it didn't support dynamic reparenting, giving
wrong colors in some cases (see black on black battery on the phone)
even tough is a bit complicated, now by cascading signals down the
children tree, support on the fly apply of the new context upon
reparenting.
also add a manual test case showing text, rectangles and icons
dynamically changing color as they get moved from one scope
to the other
REVIEW:126654
Change-Id: I3d746b73eac55a359c4706fb719b4d5018677fb5
