Added Area-Library, Triaged labels.

Removed Type-Defect, Area-Library labels.
Added Type-Enhancement, Area-Language labels.

This comment was originally written by ro...@gmail.com

To illustrate how one would do this without language support:

class Foo
{
    Foo()
    {
         checkInvariants();
         assert(/* requirement */);

         try
         {
             /* implementation /
         }
         finally
         {
              assert(/ ensures */);
              checkInvariants();
         }
    }

    void checkInvariants()
    {
         assert(/* invariant */);
    }
}

Which gives a lot of code clutter...

This comment was originally written by ronag...@gmail.com

Instead of something like:

class Foo
{
    Foo()
    {
        requires
        {
            /* requirement /
        }
        
        ensures
        {
            / ensures /
        }
        
         / implementation /
    }
    
    invariants
    {
         / invariant */;
    }
}

Added Duplicate label.
Marked as being merged into #3049.