PCBDDC: move stack variables of PCBDDCCoarseSetUp to protected block

PCBDDC: Move work vector creation to a separate routine

Now the VecType/comm of R vecs are inferred from that of vec1_N

PCBDDC: allow computation of number of vertices/constraints in GetPrimal functions without actually computing their local indices

Merge branch 'stefano_zampini/pcbddc-multipleconstraintsbugfix' into stefano_zampini/pcbddc-improvelocalsolvers

PCBDDC: further improvements to BLAS/LAPACK calls readibility

min_n replaced by k to fullfill code developing guidelines

PCBDDC: Remove aliased parameters for QR calls

Improved readibility

PCBDDC: Remove aliased parameter from DDOT call

PCBDDC: Remove aliased parameters from GEMM calls.

Improved readibility

PCBDDC: Remove aliased parameters from GESVD calls

PCBDDC: Remove aliased parameters from SYEV calls.

Improved readibility

PCBDDC: protect queries to lapack GESVD/SYEV when there are no edges or faces (1D)

PCBDDC: protect code for mirrors by graph size.

These are invalid reads in multilevel

PCBDDC: Move setup of local scatters into a routine

PCBDDC: use a boolean memory instead of scalar one to compute local scatters

PCBDDC: Setup of local matrices moved into a separate routine into bddcprivate.c

PCBDDC: better management of local matrices among repeated solves

PCBDDC: move setup of local solvers into a routine into bddcprivate.c

PCBDDCSetUseExactDirichlet moved accordingly

PCBDDC: create local solvers once. Reuse them during repeated linear solves

Destroy routines moved outside ResetSolvers routine.

PCBDDC: Added orthonormalization routine

nullspace code changed accordingly

PCBDDC: function pointers removed from FETIDP code.

Using PCPreSolve_BDDC, PCPostSolve_BDDC instead.
Added more guards in Pre and Post solves.

PCBDDC: Less tricky loop on constraints when changing the basis

PCBDDC: Constraints setup improved

- Change of basis is now performed using QR factorization of constraints
- Added missing support for complexes when PETSC_MISSING_GESVD is defined
- Improved co

PCBDDC: Constraints setup improved

- Change of basis is now performed using QR factorization of constraints
- Added missing support for complexes when PETSC_MISSING_GESVD is defined
- Improved code readability

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PCBDDC: Store special marks for local dofs in a separate memory of PCBDDCGraph (not which_dof)

PCBDDC: bugfix in PCPostSolve_BDDC.

Right hand side was not get back to its original state when change of basis was not requested.

PCBDDC: bugfix when multiple constraints are present on the same connected component

Local to global mapping of coarse dofs was badly computed