Used to select all modules including boxes, set when both `full` and `boxes` are true in the constructor, pulling down `full_selection`.
Add `Selection::selects_all()` method as short hand for `full_selection || complete_selection`.
Update selection operations to account for complete selections.
Add static methods to `Selection` for creating a new empty/full/complete selection to make it clearer to users when doing so.
Use said static methods to replace most instances of the `Selection` constructor.
Update `Selection::optimize` to use
The `Design::selected_*()` methods no longer unconditionally skip boxed modules. Instead, selections are now box and design aware.
The selection constructor now optionally takes a design pointer, and has a new `selects_boxes` flag. If the selection has an assigned design, then `Selection::selected_*()` will only return true for boxed modules if the selects_boxes flag is set. A warning is raised if a selection is checked and no design is set. Selections can change design via the `Selection::optimize()` method.
Most places that iterate over `Design::modules()` and check `Selection::selected_module()` should instead use `Design::selected_modules()`.
Since boxed modules should only ever be selected explicitly, and `full_selection` (now) refers to all non-boxed modules, `Selection::optimize()` will clear the `full_selection` flag if the `selects_boxes` flag is enabled, and instead explicitly selects all modules (including boxed modules). This also means that `full_selection` will only get automatically applied to a design without any boxed modules.
These changes necessitated a number of changes to `select.cc` in order to support this functionality when operating on selections, in particular when combining selections (e.g. by union or difference).
To minimize redundancy, a number of places that previously iterated over `design->modules()` now push the current selection to the design, use `design->selected_modules()`, and then pop the selection when done.
Introduce `RTLIL::NamedObject`, to allow for iterating over all members of a module with a single iterator instead of needing to iterate over wires, cells, memories, and processes separately.
Also implement `Module::selected_{memories, processes, members}()` to match wires and cells methods. The `selected_members()` method combines each of the other `selected_*()` methods into a single list.
