ENH: lazier demand-driven evaluation in faOption

src/faOptions/faOption/faOption.C

src/faOptions/faOption/faOption.H

src/faOptions/faOption/faOptionI.H

src/faOptions/faOption/faOptionList.H

src/faOptions/faOption/faOptionListTemplates.C

src/faOptions/faceSetOption/faceSetOption.H

...ces/derived/contactHeatFluxSource/contactHeatFluxSource.H

...s/sources/derived/externalFileSource/externalFileSource.C

...s/sources/derived/externalFileSource/externalFileSource.H

...s/derived/externalHeatFluxSource/externalHeatFluxSource.C

...s/derived/externalHeatFluxSource/externalHeatFluxSource.H

...s/sources/derived/jouleHeatingSource/jouleHeatingSource.C

...s/sources/derived/jouleHeatingSource/jouleHeatingSource.H

src/finiteArea/faMatrices/faMatricesFwd.H

src/finiteVolume/cfdTools/general/fvOptions/fvOption.C

src/finiteVolume/cfdTools/general/fvOptions/fvOption.H

src/finiteVolume/cfdTools/general/fvOptions/fvOptionI.H