clang-tidy_strict warnings for Arx in branch 1.2.1

• altera-struct-pack-align [docs] (1)
• cppcoreguidelines-special-member-functions [docs] (1)
• modernize-use-equals-default [docs] (1)
• misc-include-cleaner [docs] (3)
• modernize-use-default-member-init [docs] (3)
• performance-enum-size [docs] (3)
• misc-non-private-member-variables-in-classes [docs] (4)
• modernize-use-nodiscard [docs] (4)