databases/grass7: add SONAME and use new path for graphics/qgis*

• Add SONAME (upstreamed) [1]
• Remove the (bad) idea to keep a symlink to the old path logic (grass-M.m.b)
• Fix FindGRASS.cmake for graphics/qgis and graphics/qgis-ltr (upstreamed) [2]
  
  [1] https://github.com/OSGeo/grass/pull/301 [2] https://github.com/qgis/QGIS/pull/34088

PR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=243736
Approved by: Rainer Hurlin (maintainer), tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D23470