ART: Use reinterpret_cast{32,64}<> when appropriate.

And fix UnstartedRuntime checking for null arguments in all
functions where we now use reinterpret_cast32<>.

This is a follow-up to
    https://android-review.googlesource.com/783607 .

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Test: Pixel 2 XL boots.
Test: m test-art-target-gtest
Test: testrunner.py --target --optimizing
Bug: 117427174
Change-Id: I58f8ad59f70e3fbb1d06aef419cd26555706fa65
diff --git a/runtime/imt_conflict_table.h b/runtime/imt_conflict_table.h
index 3586864..02b3be4 100644
--- a/runtime/imt_conflict_table.h
+++ b/runtime/imt_conflict_table.h
@@ -187,17 +187,17 @@
 
   ArtMethod* GetMethod(size_t index, PointerSize pointer_size) const {
     if (pointer_size == PointerSize::k64) {
-      return reinterpret_cast<ArtMethod*>(static_cast<uintptr_t>(data64_[index]));
+      return reinterpret_cast64<ArtMethod*>(data64_[index]);
     } else {
-      return reinterpret_cast<ArtMethod*>(static_cast<uintptr_t>(data32_[index]));
+      return reinterpret_cast32<ArtMethod*>(data32_[index]);
     }
   }
 
   void SetMethod(size_t index, PointerSize pointer_size, ArtMethod* method) {
     if (pointer_size == PointerSize::k64) {
-      data64_[index] = dchecked_integral_cast<uint64_t>(reinterpret_cast<uintptr_t>(method));
+      data64_[index] = reinterpret_cast64<uint64_t>(method);
     } else {
-      data32_[index] = dchecked_integral_cast<uint32_t>(reinterpret_cast<uintptr_t>(method));
+      data32_[index] = reinterpret_cast32<uint32_t>(method);
     }
   }