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/class_linker.cc b/runtime/class_linker.cc
index b747225..f778bc5 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -8892,7 +8892,7 @@
         self,
         kDexFileIndexStart + 1));
     DCHECK(h_long_array != nullptr);
-    h_long_array->Set(kDexFileIndexStart, reinterpret_cast<intptr_t>(dex_file));
+    h_long_array->Set(kDexFileIndexStart, reinterpret_cast64<int64_t>(dex_file));
 
     // Note that this creates a finalizable dalvik.system.DexFile object and a corresponding
     // FinalizerReference which will never get cleaned up without a started runtime.