[deoptimizer] Refactor to clarify const variables in frame computation

DoComputeInterpretedFrame and friends are long and complex functions.
It is often not clear which variables are constants and which are
later modified. This CL tries to clarify, mostly by marking variables
const when possible.

Bug: v8:9534
Change-Id: Ifa73402c392ad244ab5ea37262293f8d9db98be0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1752848
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63245}

src/deoptimizer/deoptimizer.h

@@ -572,6 +572,9 @@ class Deoptimizer : public Malloced {
   // Some architectures need to push padding together with the TOS register
   // in order to maintain stack alignment.
   static bool PadTopOfStackRegister();
+  static int TopOfStackRegisterPaddingSlots() {
+    return PadTopOfStackRegister() ? 1 : 0;
+  }
 
   // Searches the list of known deoptimizing code for a Code object
   // containing the given address (which is supposedly faster than