ENH: expose fieldNames() selection for sampledSets/sampledSurfaces

- consistent with probes. Allows reporting/querying

applications/test/surface-sampling/Test-surface-sampling.C

@@ -184,7 +184,15 @@ int main(int argc, char *argv[])
     // Construct from Time and dictionary, without loadFromFiles
     sampledSurfaces sampling("test-sample", runTime, *sampleDict);
 
-    Info<< "Loaded " << sampling.size() << " surface samplers" << nl;
+    #if (OPENFOAM <= 2306)
+    Info<< "Loaded " << sampling.size() << " surface samplers, fields: "
+        << flatOutput(sampleDict->getOrDefault<wordRes>("fields", wordRes()))
+        << nl;
+    #else
+    Info<< "Loaded " << sampling.size() << " surface samplers, fields: "
+        << flatOutput(sampling.fieldNames())
+        << nl;
+    #endif
 
     if (sampling.empty())
     {

src/sampling/sampledSet/sampledSets/sampledSets.H

@@ -306,6 +306,9 @@ public:
         //  \return old value
         bool verbose(const bool on) noexcept;
 
+        //- Return names of fields to sample
+        const wordRes& fieldNames() const noexcept { return fieldSelection_; }
+
         //- Read the sampledSets
         virtual bool read(const dictionary&);
 

src/sampling/sampledSurface/sampledSurfaces/sampledSurfaces.H

@@ -349,6 +349,9 @@ public:
         //  \return old value
         bool verbose(const bool on) noexcept;
 
+        //- Return names of fields to sample
+        const wordRes& fieldNames() const noexcept { return fieldSelection_; }
+
         //- Read the sampledSurfaces dictionary
         virtual bool read(const dictionary& dict);