Merge topic 'function-var-current'

24fdd51f45 Refactor: Replace CMAKE_CURRENT_LIST_DIR with CMAKE_CURRENT_FUNCTION_LIST_DIR
90e3e2a777 cmFunctionCommand: Introduce `CMAKE_CURRENT_FUNCTION*` variables
dd54290dab Refactor: Modernize `function` command

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Ben Boeckel <ben.boeckel@kitware.com>
Merge-request: !4000