ART: Introduce thread-current-inl.h

Factor out Thread::Current() code into its own -inl file to remove
transitive includes.

This requires at the same time correcting mutex.h, i.e., moving
some functions into mutex-inl.h.

Test: m test-art-host
Change-Id: I88f888b604e0897368d9b483edce6ce4332dd9c9
diff --git a/runtime/dex_file_test.cc b/runtime/dex_file_test.cc
index 1d4507a..78d5c5f 100644
--- a/runtime/dex_file_test.cc
+++ b/runtime/dex_file_test.cc
@@ -27,7 +27,7 @@
 #include "mem_map.h"
 #include "os.h"
 #include "scoped_thread_state_change-inl.h"
-#include "thread-inl.h"
+#include "thread-current-inl.h"
 #include "utils.h"
 
 namespace art {