Fixes for many clang-tidy bugprone-* checks

[thehans]

Some counts of unique lines which failed bugprone checks before:

    336 [bugprone-narrowing-conversions]
     78 [bugprone-easily-swappable-parameters]
     19 [bugprone-branch-clone]
     19 [bugprone-reserved-identifier]
     14 [bugprone-implicit-widening-of-multiplication-result]
      9 [bugprone-macro-parentheses]
      7 [bugprone-use-after-move]
      6 [bugprone-virtual-near-miss]
      5 [bugprone-exception-escape]
      4 [bugprone-suspicious-enum-usage]
      2 [bugprone-copy-constructor-init]
      1 [bugprone-parent-virtual-call]
      1 [bugprone-misplaced-widening-cast]
      1 [bugprone-integer-division]
      1 [bugprone-forwarding-reference-overload]

after:

    330 [bugprone-narrowing-conversions]
     78 [bugprone-easily-swappable-parameters]
      5 [bugprone-exception-escape]

The remaining checks are disabled in the top-level .clang-tidy file:

• narrowing-conversions were just too many to deal with
• easily-swappable-parameters This is triggered any time two or more parameters of the same type are adjacent in a function signature, for example anything of the form: foo(T x,T y,T z). I don't see any sensible way to avoid such occurrences.
• exception-escape these should probably be looked into, but I'm not sure how to best handle them. The offending lines are pasted below.

src/core/Context.h:27:3: warning: an exception may be thrown in function '~ContextHandle<T>' which should not throw exceptions [bugprone-exception-escape]
src/core/Context.h:40:18: warning: an exception may be thrown in function 'operator=' which should not throw exceptions [bugprone-exception-escape]
src/core/ContextMemoryManager.cc:350:23: warning: an exception may be thrown in function '~ContextMemoryManager' which should not throw exceptions [bugprone-exception-escape]
src/core/ContextMemoryManager.h:36:3: warning: an exception may be thrown in function '~ContextMemoryManager' which should not throw exceptions [bugprone-exception-escape]
src/openscad.cc:886:5: warning: an exception may be thrown in function 'main' which should not throw exceptions [bugprone-exception-escape]