[vm, profiler] Also use alignment to detect invalid frame pointers.

TEST=ubsan
Change-Id: Ie4742c82c2ca5de5e4283914dd5098bf4c325e5b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/375063
Reviewed-by: Alexander Aprelev <[email protected]>
Commit-Queue: Ryan Macnak <[email protected]>

Author: rmacnak-google

runtime/vm/profiler.cc

@@ -310,6 +310,9 @@ class ProfilerNativeStackWalker : public ProfilerStackWalker {
     if (fp == nullptr) {
       return false;
     }
+    if (!Utils::IsAligned(fp, kWordSize)) {
+      return false;
+    }
     uword cursor = reinterpret_cast<uword>(fp);
     cursor += sizeof(fp);
     bool r = (cursor >= lower_bound_) && (cursor < stack_upper_);