pgsql: Refactor code creating PartitionBoundInfo

Refactor code creating PartitionBoundInfo

The code building PartitionBoundInfo based on the constituent partition
data read from catalogs has been located in partcache.c, with a specific
set of routines dedicated to bound types, like sorting or bound data
creation.  All this logic is moved to partbounds.c and relocates all the
bound-specific logistic into it, with partition_bounds_create() as
principal entry point.

Author: Amit Langote
Reviewed-by: Michael Paquier, Álvaro Herrera
Discussion: https://postgr.es/m/3f289da8-6d10-75fe-814a-635e8b191d43@lab.ntt.co.jp

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b52b7dc250bba74fbaed685af4a37b450a0e2726

Modified Files
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src/backend/partitioning/partbounds.c | 627 +++++++++++++++++++++++++++++++++-
src/backend/utils/cache/partcache.c   | 539 ++---------------------------
src/include/partitioning/partbounds.h |  44 +--
3 files changed, 661 insertions(+), 549 deletions(-)