[feature] add support for non-zero starting index

Add support in dense layouts for non-zero, negative even, starting
indices (bases). Include accessor functions and a shift operator that
can change those bases.
6 jobs for nonzero-centered-indices in 2 minutes and 58 seconds
latest
Status Job ID Name Coverage
  Style
failed #48316
integration
checkpatch

00:01:31

passed #48315
integration
repoquality

00:02:58

passed #48317
integration
style:docs

00:01:42

 
  Build
skipped #48318
make:generic
skipped #48320
knl
make:knl
skipped #48319
make:out-of-tree
 
Name Stage Failure
failed
checkpatch Style
include/aml.h:331: WARNING: line over 80 characters
include/aml.h:341: WARNING: line over 80 characters
src/layout/dense.c:240: WARNING: Missing a blank line after declarations
src/layout/dense.c:241: ERROR: space required before the open parenthesis '('
src/layout/dense.c:493: WARNING: Missing a blank line after declarations
src/layout/dense.c:494: ERROR: space required before the open parenthesis '('
src/layout/layout.c:28: ERROR: space required before the open parenthesis '('
src/layout/layout.c:30: WARNING: Missing a blank line after declarations
ERROR: Job failed: exit status 1