C++: Fix names of functions dealing with enclosing scopes

...in order to better tell apart the type related functions
isScope()/asScope() and the functions dealing with enclosing scopes:

    * scope() --> enclosingScope()
    * setScope() --> setEnclosingScope()
    * resetScope() --> resetEnclosingScope()

Change-Id: Id743a7d1b6a1a1a0ffcd8568cbd8ebbdfc16eaa1
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>