ENH: Time: use constant(), time() instead of hardcoded strings

applications/test/fvSolutionCombine/Test-fvSolutionCombine.C

...s/utilities/mesh/conversion/foamToStarMesh/getTimeIndex.H

...ns/utilities/mesh/conversion/foamToSurface/getTimeIndex.H

...ocessing/dataConversion/foamToEnsightParts/getTimeIndex.H

...graphics/PV3Readers/PV3FoamReader/vtkPV3Foam/vtkPV3Foam.C

src/OpenFOAM/db/Time/Time.C

src/OpenFOAM/db/Time/Time.H

src/OpenFOAM/db/Time/findTimes.C

src/OpenFOAM/db/Time/timeSelector.C

src/OpenFOAM/db/Time/timeSelector.H

src/conversion/meshReader/meshReader.C

src/conversion/meshReader/meshReaderAux.C

src/conversion/meshWriter/starcd/STARCDMeshWriter.C

src/edgeMesh/edgeMeshFormats/edgeMeshFormatsCore.C

src/meshTools/coordinateSystems/coordinateSystems.C

src/surfMesh/surfaceFormats/surfaceFormatsCore.C

src/triSurface/triSurface/triSurface.C