CHANGED: The text variable ${SHEETNAME} now always represents the name of the
sheet when used anywhere in the schematic editor, including the title block
ADDED: A new text variable ${SHEETPATH} which is replaced with the path to the
current sheet - e.g. "/Sheet 1/Sheet 2".
To ensure backward compatibility, the default drawing sheet now uses
${SHEETPATH}. Custom drawing sheets will need to be manually edited.
User-defined variables cannot be used for internally-reserved variables
Fixes https://gitlab.com/kicad/code/kicad/issues/11232
(cherry picked from commit c23679d9bdc3347c441d3e4a9460747012b510ad)
