Make ensureOutputDirExists() callable outside readDeck.cpp, and use it.

This is necessary because when using Damaris we must have the output dir ready
when we initialize Damaris. In the existing code, this was ensured only
from the setupLogging() call.

opm/simulators/utils/readDeck.cpp

@@ -93,23 +93,6 @@ namespace {
             ->setMessageLimiter(std::make_shared<Opm::MessageLimiter>(10, limits));
     }
 
-    void ensureOutputDirExists_(const std::string& cmdline_output_dir)
-    {
-        namespace fs = std::filesystem;
-
-        if (! fs::is_directory(cmdline_output_dir)) {
-            try {
-                fs::create_directories(cmdline_output_dir);
-            }
-            catch (...) {
-                throw std::runtime_error {
-                    fmt::format("Creation of output directory '{}' failed",
-                                cmdline_output_dir)
-                };
-            }
-        }
-    }
-
     void loadObjectsFromRestart(const Opm::Deck&                     deck,
                                 const Opm::Parser&                   parser,
                                 const Opm::ParseContext&             parseContext,
@@ -376,6 +359,24 @@ namespace {
 
 // ---------------------------------------------------------------------------
 
+
+void Opm::ensureOutputDirExists(const std::string& cmdline_output_dir)
+{
+    namespace fs = std::filesystem;
+
+    if (! fs::is_directory(cmdline_output_dir)) {
+        try {
+            fs::create_directories(cmdline_output_dir);
+        }
+        catch (...) {
+            throw std::runtime_error {
+                fmt::format("Creation of output directory '{}' failed",
+                            cmdline_output_dir)
+                    };
+        }
+    }
+}
+
 // Setup the OpmLog backends
 Opm::FileOutputMode
 Opm::setupLogging(const int          mpi_rank_,
@@ -387,7 +388,7 @@ Opm::setupLogging(const int          mpi_rank_,
                   const bool         allRanksDbgLog)
 {
     if (!cmdline_output_dir.empty()) {
-        ensureOutputDirExists_(cmdline_output_dir);
+        ensureOutputDirExists(cmdline_output_dir);
     }
 
     // create logFile

opm/simulators/utils/readDeck.hpp

@@ -57,6 +57,10 @@ enum class FileOutputMode {
     OUTPUT_ALL = 3,
 };
 
+// Ensure that a directory exists, creating it if it does not.
+void
+ensureOutputDirExists(const std::string& cmdline_output_dir);
+
 // Setup the OpmLog backends
 FileOutputMode
 setupLogging(int                mpi_rank_,