Use database extensionals instead of their wrapper classes in two predicates

We are planning to change the charpred of `Function` in the CodeQL C++ library,
which means the code changed here will no longer compile. By switching to the
extensionals, the code will keep compiling.

DIL before:
```
noinline
`ConstantExprs::isFunction/1#600714be`(
  /* Element::Element */ interned unique entity el
)
{
  exists(interned dontcare string _, interned dontcare int _1 |
    functions(el, _, _1)
  ) or
  exists(interned dontcare int _ | exprparents(el, _, el))
}

noopt
`ConstantExprs::callHasNoTarget/1#e6e8caa4`(
  /* @funbindexpr */ interned unique entity fc
)
{
  exists(/* Function::Function */ interned entity f |
    funbind(fc, f) and not(`ConstantExprs::isFunction/1#600714be`(f))
  )
}
```

DIL after:
```
noinline
`ConstantExprs::isFunction/1#600714be`(/* @element */ interned unique entity el)
{
  exists(interned dontcare string _, interned dontcare int _1 |
    functions(el, _, _1)
  ) or
  exists(interned dontcare int _ | exprparents(el, _, el))
}

noopt
`ConstantExprs::callHasNoTarget/1#e6e8caa4`(
  /* @funbindexpr */ interned unique entity fc
)
{
  exists(/* @function */ interned entity f |
    funbind(fc, f) and not(`ConstantExprs::isFunction/1#600714be`(f))
  )
}
```

Author: jketema

cpp/common/src/codingstandards/cpp/enhancements/ControlFlowGraphEnhancements.qll

@@ -10,8 +10,8 @@ import cpp
  * should be in this relation.
  */
 pragma[noinline]
-private predicate isFunction(Element el) {
-  el instanceof Function
+private predicate isFunction(@element el) {
+  el instanceof @function
   or
   el.(Expr).getParent() = el
 }
@@ -22,7 +22,7 @@ private predicate isFunction(Element el) {
  */
 pragma[noopt]
 private predicate callHasNoTarget(@funbindexpr fc) {
-  exists(Function f |
+  exists(@function f |
     funbind(fc, f) and
     not isFunction(f)
   )