Move xfa/fwl/core to xfa/fwl.

The core/ directory in FWL no-longer provides any context. This Cl moves all
of the core/ files up to the fwl/ folder.

As well, the CFWL_EvtFoo files are renamed CFWL_EventFoo and the CFWL_MsgFoo
files are renamed CFWL_MessageFoo. The event and message preceed the type in
order to keep the files sorted together and to make it clear that they're all
related.

Review-Url: https://codereview.chromium.org/2559173002
diff --git a/fpdfsdk/DEPS b/fpdfsdk/DEPS
index ce037d9..e077225 100644
--- a/fpdfsdk/DEPS
+++ b/fpdfsdk/DEPS
@@ -2,7 +2,7 @@
   '+core',
   '+public',
   '+v8',
-  '+xfa/fwl/core',
+  '+xfa/fwl',
   '+xfa/fxbarcode',
   '+xfa/fxfa',
   '+xfa/fxgraphics',