[turbofan] Add dynamic sized GraphAssemblerLabels

The GraphAssemblerLabel VarCount template parameter now can have a
marker value ~0 which is marker for it being dynamic sized -- this means
that a bit of template magic turns its std::arrays into std::vectors.
Merging GraphAssemblerLabels works by duck-typing access to these
arrays/vectors.

These dynamic GraphAssemblerLabels are created whenever a single

GraphAssemblerLabels being created when instead a list of values
convertible to MachineRepresentation is passed in. Passing anything else
will result in a GraphAssemblerLabel with marker value ~1, which is
considered "invalid" and will give a compilation error down the line.

std: :vector is passed into MakeLabel, with the static
Change-Id: I833bdedac2f8e26fcc88aa59dd67b7e4b1c4296d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3913349
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83424}

src/compiler/js-call-reducer.cc

@@ -744,10 +744,7 @@ class IteratingArrayBuiltinReducerAssembler : public JSCallReducerAssembler {
       TNode<Vars>... vars) {
     if (!IsHoleyElementsKind(kind)) return o;
 
-    std::array<MachineRepresentation, sizeof...(Vars)> reps = {
-        MachineRepresentationOf<Vars>::value...};
-    auto if_not_hole =
-        MakeLabel<sizeof...(Vars)>(reps, GraphAssemblerLabelType::kNonDeferred);
+    auto if_not_hole = MakeLabel(MachineRepresentationOf<Vars>::value...);
     BranchWithHint(HoleCheck(kind, o), continue_label, &if_not_hole,
                    BranchHint::kFalse, vars...);