- attributes such as assignable(), coupled() etc
- common patchField types: calculatedType(), zeroGradientType() etc.
This simplifies reference to these types without actually needing a
typed patchField version.
ENH: add some basic patchField types to fieldTypes namespace
- allows more general use of the names
ENH: set extrapolated/calculated from patchInternalField directly
- avoids intermediate tmp
- simplifies construction/inheritance
ENH: add {fa,fv}PatchField::zeroGradientType() static
- can be used to avoid literal "zeroGradient" in places
STYLE: adjust naming of pointPatch runtime selection table
- simply use 'patch' as per fa/fv fields
STYLE: add zero-size guard to patch constraintType(const word&)
It is better to declare the namespace of each function in the C file
rather than "open" the namespace as this may lead to inconsistencies
between the declaration in the H files and definition in the C file.
