[GeoMechanicsApplication] Revise water loads conditions

[indigocoral]

Currently there are many processes that compute the hydrostatic water pressure:
on a boundary:
2D
ApplyConstantBoundaryHydrostaticPressureProcess
ApplyBoundaryHydrostaticPressureTableProcess
ApplyConstantBoundaryPhreaticLinePressureProcess
ApplyBoundaryPhreaticLinePressureTableProcess
note that the multi line is missing.
3D
ApplyConstantBoundaryPhreaticSurfacePressureProcess
ApplyBoundaryPhreaticSurfacePressureTableProcess

On a domain:
2D
ApplyConstantHydrostaticPressureProcess
ApplyHydrostaticPressureTableProcess
ApplyConstantPhreaticLinePressureProcess
ApplyPhreaticLinePressureTableProcess
ApplyConstantPhreaticMultiLinePressureProcess
ApplyPhreaticMultiLinePressureTableProcess
3D
ApplyConstantPhreaticSurfacePressureProcess
ApplyPhreaticSurfacePressureTableProcess

They all implement projection in gravity of a point onto a phreatic surface and computation of the resulting water pressure.

Proposed unified implementation:
Let the user give a point or series of points on the phreatic surface, gravity direction and water weight ( rho*g ) and possibly a suction cutoff value
2D:

• sort the points to form a line in horizontal direction
  3D
• form a triangulated surface ( this is the tricky part, we may need tools for this and I propose to do this later and separately, so handle the 2D first )
  followed by
• apply phreatic surface coordinate changes due to given tables
• compute projection and distance of point to the constructed phreatic surface. Let points outside the domain get the nearest given point value. ( don't extrapolate)
• convert distance to water pressure ( zero or suction cutoff above phreatic surface, hydrostatic below phreatic surface

known hurdle: The json file reader from Kratos does not seem to process a list of point coordinates. In the existing PhreaticMulitLine this is solved in an ugly manner by providing X, Y and Z-coordinates in separate lists.

[rfaasse]

@WPK4FEM will split this parent issue into sub-issues