Remove duplicate instance data saved in both root SCH_SCREEN and SCH_SHEET
objects that was causing them to be out of sync. All sheet instance data
is stored in the SCH_SHEET object itself and rebuilt on the fly so it is
always current.
Remove Get/SetPageNumber from SCH_SHEET_PATH object so it doesn't obfuscate
where the actual sheet page number information exists.
Fixes https://gitlab.com/kicad/code/kicad/-/issues/9782
1) Generalize SCH_ITEM owners (SCH_COMPONENT, SCH_SHEET, and now
SCH_GLOBALLABEL)
2) Generalize hypertext items
3) Use SCH_FIELD autoplace infrastructure for placing intersheet
references
4) Use textVar infrastructure for buildin intersheet references.
As an important side-effect this also fixes the undo issues with
intersheet refs.
The groundwork has now been laid for per sheet instance data. Initially
this only supports sheet page numbers but could be expanded to include
other per sheet instance information.
ADDED: Support for user defined schematic page numbers.
Wayne Stambaugh
Marek Roszko
Jeff Young