pgsql: Implement various jsonpath methods

Implement various jsonpath methods

This commit implements ithe jsonpath .bigint(), .boolean(),
.date(), .decimal([precision [, scale]]), .integer(), .number(),
.string(), .time(), .time_tz(), .timestamp(), and .timestamp_tz()
methods.

.bigint() converts the given JSON string or a numeric value to
the bigint type representation.

.boolean() converts the given JSON string, numeric, or boolean
value to the boolean type representation. In the numeric case, only
integers are allowed. We use the parse_bool() backend function
to convert a string to a bool.

.decimal([precision [, scale]]) converts the given JSON string
or a numeric value to the numeric type representation. If precision
and scale are provided for .decimal(), then it is converted to the
equivalent numeric typmod and applied to the numeric number.

.integer() and .number() convert the given JSON string or a
numeric value to the int4 and numeric type representation.

.string() uses the datatype's output function to convert numeric
and various date/time types to the string representation.

The JSON string representing a valid date/time is converted to the
specific date or time type representation using jsonpath .date(),
.time(), .time_tz(), .timestamp(), .timestamp_tz() methods. The
changes use the infrastructure of the .datetime() method and perform
the datatype conversion as appropriate. Unlike the .datetime()
method, none of these methods accept a format template and use ISO
DateTime format instead. However, except for .date(), the
date/time related methods take an optional precision to adjust the
fractional seconds.

Jeevan Chalke, reviewed by Peter Eisentraut and Andrew Dunstan.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/66ea94e8e606529bb334515f388c62314956739e

Modified Files
--------------
doc/src/sgml/func.sgml | 218 +++
src/backend/catalog/sql_features.txt | 28 +-
src/backend/utils/adt/jsonpath.c | 138 +-
src/backend/utils/adt/jsonpath_exec.c | 718 +++++++++-
src/backend/utils/adt/jsonpath_gram.y | 78 +-
src/backend/utils/adt/jsonpath_scan.l | 11 +
src/include/utils/jsonpath.h | 11 +
src/test/regress/expected/jsonb_jsonpath.out | 1848 +++++++++++++++++++++++++-
src/test/regress/expected/jsonpath.out | 78 ++
src/test/regress/sql/jsonb_jsonpath.sql | 492 +++++++
src/test/regress/sql/jsonpath.sql | 13 +
11 files changed, 3586 insertions(+), 47 deletions(-)