vec/qf - initial valid/borrowed/owned split for data (#853)

* vec/qf - initial valid/borrowed/owned split for data

* vec/qf - tidy logic for checking active/stale data

* minor - add missing NU

vec/qf - initial valid/borrowed/owned split for data (#853)

* vec/qf - initial valid/borrowed/owned split for data

* vec/qf - tidy logic for checking active/stale data

* minor - add missing NULL

* doc - explain VectorTakeArray update

* minor - update error messages

* test - update error message in junit/tap

* gpu - fix stray CeedScalar vs void for QFunctionContext

* vec/qf - clarify/simplify access logic

* vec - calloc host arrays when no value set to make empty

* style - minor

* style - minor

* minor - fix error messages

* vec/qf - move data validity checking to backend interface

* gpu - add missing sync error checking for qfcontext

* gpu - homogonize use of impl for backend data to reduce confusion

* vec - clarify access conditions

* python - update test for stricter vector access

* vec - minor fixes

* minor - fix ipython change

* vec - add missing declarations in ceed/backend.h

* ctx - mirror vector borrowed data check in ctx interface

* vec - add CeedVectorGetArrayWrite

* vec - consistent use of CeedVectorGetArray vs CeedVectorGetArrayWrite

* python - small vec fixes

* doc - describe vector data semantics

* magma - update restriction

* gpu - fix restr bug I added, need to sum into target

* magma - fix restriction bug

* cpu - fix restriction bug here too

* op - fix evec allocations

* julia - fix ElemRestriction for new vector access rules

* op - double check GetArray vs Read vs Write usage

* doc - small fix

* restr - clean up read/write logic for restr

* python - add vec.array_write

* magma - typo fix

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