Rename App to Env where needed.

More instances of CPDFSDK_Environment being called m_pApp in the code. Renamed
to m_pEnv to be clear that it's the environment not an app object.

Review-Url: https://codereview.chromium.org/2354413002
diff --git a/fpdfsdk/javascript/cjs_runtime.h b/fpdfsdk/javascript/cjs_runtime.h
index 12f902d..da7e384 100644
--- a/fpdfsdk/javascript/cjs_runtime.h
+++ b/fpdfsdk/javascript/cjs_runtime.h
@@ -42,7 +42,7 @@
   int ExecuteScript(const CFX_WideString& script,
                     CFX_WideString* info) override;
 
-  CPDFSDK_Environment* GetReaderApp() const { return m_pApp; }
+  CPDFSDK_Environment* GetReaderEnv() const { return m_pEnv; }
 
   // Returns true if the event isn't already found in the set.
   bool AddEventToSet(const FieldEvent& event);
@@ -63,7 +63,7 @@
   void DefineJSObjects();
 
   std::vector<std::unique_ptr<CJS_Context>> m_ContextArray;
-  CPDFSDK_Environment* const m_pApp;
+  CPDFSDK_Environment* const m_pEnv;
   CPDFSDK_Document* m_pDocument;
   bool m_bBlocking;
   bool m_isolateManaged;