databases/grass7, math/saga, graphics/qgis and graphics/qgis-ltr: update to latest versions

• math/saga:
  • Update to 7.6.2
  • Use wxWidgets 3.0+ instead of 3.1+ since 3.1 is not a mandatory version and this reduces the number of packages installed when you install saga and qgis/grass (which requires version 3.0).
• databases/grass7:
  • Update to 7.8.2 first version for python3 only
  • Use ${PY_NUMPY} variable
  • Readd openmp
  • Use wxPython40 for python3
  • Remove bash dependency. You can use any shell.
  • Rework the workaround in post-install (for / touch files). Fix the long (random) standing issue with pkg-plist
  • Alphabetize USES and OPTIONS
  • Replace XX_configure_on by XX_configure_with as possible
• graphics/qgis:
  • Update to 3.12.1
  • Remove patches (applied upstream or fixed in ports: pyqt5 / sip)
• graphics/qgis-ltr:
  • Update to 3.10.4

PR: 241892, 244979
Reported by: rainer hurling (maintainer), lbartoletti (maintainer)
Reviewed by: tcberner (mentor), rainer hurling (maintainer)
Approved by: tcberner (mentor), rainer hurling (maintainer)
Differential Revision: https://reviews.freebsd.org/D24198