clang-tidy: add modernize nullptr & emplace

clang-tidy: add modernize nullptr & emplace

Move selection/scanner.cpp and parser.cpp into
libgromacs_generated to exclude it from clang-tidy.

All files had been automatically fixed previously.
Changes are new occurrences of old pattern.

Change-Id: I46df2622b555af83e03cc79077d3510168ffc6d4