Added: Init TermuxShellEnvironment at app startup

This will currently cache `TermuxAppShellEnvironment` so that its not regenerated for each shell started since it contains some slightly expensive operations.

app/src/main/java/com/termux/app/TermuxApplication.java

@@ -60,6 +60,9 @@ public class TermuxApplication extends Application {
             }
 
             TermuxAmSocketServer.setupTermuxAmSocketServer(context);
+
+        // Init TermuxShellEnvironment constants and caches after everything has been setup including termux-am-socket server
+        TermuxShellEnvironment.init(this);
         }
     }