Improvement to TPFA

[karimifard]

The discretization must provide accurate two-point flux approximation for PEBI and orthogonal grids. Provide approximation for mesh elements with nonplanar faces. Remain compatible with existing explicit and embedded discrete fracture representation. Approximate use of full tensor permeability for TPFA.

List of features/capabilities:

MPFA Cleaning:

• [x] Merge https://github.com/GEOSX/GEOSX/pull/1925 @CusiniM
• [ ] Clean up MPFA implementation: remove MPFA stencil and revisit all variables in stencil objects to make sure they are appropriate for the new goals. @CusiniM

Inputs (1/2):

• [ ] Importing collocation points (for pressure, saturation, temperature, etc...). @francoishamon @karimifard
• [ ] Define permeability as a 2nd order tensor in the code (as an intermediate step). @karimifard

Computational geometry tools:

• [ ] Construction of the closest flat polygon to a nonplanar polygon (interfaces and fractures). @karimifard
• [ ] Distance to plane and line. @karimifard
• [ ] Computation of directional permeability using tensor permeability and interface normal. @karimifard
• [ ] Unit tests @karimifard @TotoGaz

Discretization TPFA

• [ ] Modify permeability to be a full tensor and refactor stencil's weights computations. @karimifard
• [ ] Add unit and integrated tests for it. @karimifard @CusiniM @TotoGaz

Inputs (2/2):

• [ ] Importing full scalar/vector/2nd order tensor property (Generate a second order tensor object and see how it behaves on GPU). Will be used for permeability field. Applicable to thermal conductivity... @CusiniM @TotoGaz @castelletto1
• [ ] Upgrading the vtk input file format to better fit fracture needs (using multi-block or partitioned datasets)? @TotoGaz

Import of TPFA connectivities. (long term objective)

• [ ] Importing TPFA connectivity and pore volume list (in case we bypass the TPFA discretization steps).
• [ ] Graph based ghosting strategy.