pgsql: Enforce cube dimension limit in all cube construction functions

Enforce cube dimension limit in all cube construction functions

contrib/cube has a limit to 100 dimensions for cube datatype. However, it's
not enforced everywhere, and one can actually construct cube with more than
100 dimensions having then trouble with dump/restore. This commit add checks
for dimensions limit in all functions responsible for cube construction.
Backpatch to all supported versions.

Reported-by: Andrew Gierth
Discussion: https://postgr.es/m/87va7uybt4.fsf%40news-spur.riddles.org.uk
Author: Andrey Borodin with small additions by me
Review: Tom Lane
Backpatch-through: 9.3

Branch
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REL9_3_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/9f3ade1a6f62dd0315aa14b615666e0d54054763

Modified Files
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contrib/cube/cube.c | 34 ++++++++++++++++++++++++++++++++++
contrib/cube/expected/cube.out | 40 ++++++++++++++++++++++++++++++++++++++++
contrib/cube/sql/cube.sql | 18 +++++++++++++++++-
3 files changed, 91 insertions(+), 1 deletion(-)