Instead of SortingProxyModel having a column+order, we move that state
to AbstractView. When you click on a column header, the view tells the
model to resort the relevant column with the new order.
This is implemented in SortingProxyModel by simply walking all the
reified source/proxy mappings and resorting their row indexes.
We now create multiple levels of internal mappings between source
and proxy indexes, to support tree models.
This breaks selection update after resort, which we'll have to
deal with somehow.
This patch adds SortingProxyModel::less_than(ModelIndex, ModelIndex)
which is now used to implement the sort order. This allows you to
subclass SortingProxyModel if you want to tweak how sorting works.
Get rid of the awkward case sensitivity logic in SortingProxyModel
since that can now be done outside. Turns out nobody was actually
using it anyway, but it seems like something we will want to do
in the future someday.
This is really just a workaround to keep SystemMonitor's process table
working right wrt selection retention during resorts (while also doing
full index invalidation on things like ProfileViewer inversion.)
It's starting to feel like the model abstraction is not super great
and we'll need a better approach if we want to actually build some more
dynamic functionality into our views.
Now it actually defaults to "a < b" comparison, instead of forcing you
to provide a trivial less-than comparator. Also you can pass in any
collection type that has .begin() and .end() and we'll sort it for you.
There is some sort of issue with using a SortingProxyModel together
with ColumnsView. This is a workaround to allow FilePicker to use a
MultiView for now, but this needs to be fixed separately somehow.
