Add info about noexcept into duchain

Martin Bednarrequested to merge
bednar/kdevelop:noexcept_functions into master
  1. Expose noexcept to the DUChain
  2. Fix explicit detection
  3. move virtual and explicit from AbstractFunctionDeclaration to ClassMemberDeclaration

point 3: I just saw the todo while fishing where to put noexcept...

BUG: 403798

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