ART: Change return types of field access entrypoints

Ensure that return types guarantee full-width data as the compiled
code and mterp expect by using size_t and ssize_t.

This fixes Clang no longer sign-/zero-extending small return types.

Bug: 30232671
Test: m ART_TEST_RUN_TEST_NDEBUG=true ART_TEST_INTERPRETER=true test-art-host-run-test
Change-Id: Ic505befc6c94e2dccbc8abf2b13d4c2d662e68d1
diff --git a/runtime/interpreter/interpreter.cc b/runtime/interpreter/interpreter.cc
index 8c42b3a..f1f7f42 100644
--- a/runtime/interpreter/interpreter.cc
+++ b/runtime/interpreter/interpreter.cc
@@ -324,7 +324,7 @@
       } else {
         while (true) {
           // Mterp does not support all instrumentation/debugging.
-          if (MterpShouldSwitchInterpreters()) {
+          if (MterpShouldSwitchInterpreters() != 0) {
             return ExecuteSwitchImpl<false, false>(self, code_item, shadow_frame, result_register,
                                                    false);
           }