ART: Factor out IMT from ArtMethod

Move IMT Conflict Table to its own file. Move IMT index computation to
ImTable.

In preparation for code using this independent of specific ArtMethods.

Bug: 31594153
Test: m test-art-host
Change-Id: Ifd6e304bb86724c5284984c4655c43d3af357f84
diff --git a/compiler/image_writer.cc b/compiler/image_writer.cc
index ad881b7..6b5758b 100644
--- a/compiler/image_writer.cc
+++ b/compiler/image_writer.cc
@@ -45,6 +45,7 @@
 #include "gc/space/space-inl.h"
 #include "globals.h"
 #include "image.h"
+#include "imt_conflict_table.h"
 #include "intern_table.h"
 #include "linear_alloc.h"
 #include "lock_word.h"