Remove IWFL_WidgetMgr in favor of CFWL_WidgetMgr

xfa.gyp

 {
   "variables": {
     "pdf_enable_v8%": 1,
   },
   "target_defaults": {
     "defines": [
       "PDF_ENABLE_XFA",
     ],
     'msvs_disabled_warnings': [
       4005, 4018, 4146, 4333, 4345, 4267,
@@ skipping 177 matching lines @@
         "xfa/fwl/core/fwl_widgetmgrimp.cpp",
         "xfa/fwl/core/fwl_widgetmgrimp.h",
         "xfa/fwl/core/ifwl_app.h",
         "xfa/fwl/core/ifwl_dataprovider.h",
         "xfa/fwl/core/ifwl_form.h",
         "xfa/fwl/core/ifwl_themeprovider.h",
         "xfa/fwl/core/ifwl_timer.h",
         "xfa/fwl/core/ifwl_tooltiptarget.h",
         "xfa/fwl/core/ifwl_widget.h",
         "xfa/fwl/core/ifwl_widgetdelegate.h",
-        "xfa/fwl/core/ifwl_widgetmgr.h",
         "xfa/fwl/core/include/fwl_widgethit.h",
         "xfa/fwl/core/include/ifwl_adaptertimermgr.h",
         "xfa/fwl/lightwidget/cfwl_barcode.cpp",
         "xfa/fwl/lightwidget/cfwl_barcode.h",
         "xfa/fwl/lightwidget/cfwl_checkbox.cpp",
         "xfa/fwl/lightwidget/cfwl_checkbox.h",
         "xfa/fwl/lightwidget/cfwl_combobox.cpp",
         "xfa/fwl/lightwidget/cfwl_combobox.h",
         "xfa/fwl/lightwidget/cfwl_datetimepicker.cpp",
         "xfa/fwl/lightwidget/cfwl_datetimepicker.h",
@@ skipping 540 matching lines @@
           "sources": [],
         }],
         ["OS == 'mac'", {
           "configurations": {},
           "sources": [],
         }],
       ]
     }
   ]
 }