State what a wrapper passes for an argument left to its NULL default

[estebanzimanyi]

A SQL signature states in nullDefaultBinds, for each argument declared DEFAULT NULL, what its
wrapper passes the MEOS function when the call leaves that argument out, which PostgreSQL passes
as NULL: tintSeqSetGaps(tint[], maxt interval DEFAULT NULL, maxdist float DEFAULT NULL) passes
maxt NULL and maxdist -1.0, tcbufferSeq(tcbuffer, text DEFAULT NULL) passes the interpolation
INTERP_NONE, raquetRead(text, quadbin DEFAULT NULL) passes the quadbin 0.
attach_null_default_binds of parser/boundargs.py reads each value from the wrapper: the literal a
local starts from and replaces only under PG_NARGS() > k (#_guarded_default), the interpolation
of the signature's temporal type it takes when the call carries no k (#_type_choice), or the
literal of x = PG_ARGISNULL(k) ? literal : ...; it states a position only when every parameter
the argument feeds (#_caller_index) has one, and only on a signature whose CREATE FUNCTION is not
STRICT, since a STRICT one answers NULL without calling the wrapper. _create_fn_stmts of
parser/sqlfn.py reports the strictness of a statement on request, which _wrapper_sql_strict
keys as #_signature_wrapper matches a signature.

Witness: on MEOS-API master 8818c00 over MobilityDB master 647acbe4ed the catalog states
argDefaults NULL for 74 signatures and nothing of what their wrappers pass for them, so a binding
either refuses the shorter call, as the typed Spark and Flink surfaces of JMEOS refuse
tintSeqSetGaps(tint[], interval), or passes the default of the C type, as the Spark UDF of
raquetRead passes 0 for a quadbin by coincidence.

Measured over MobilityDB master 647acbe4ed: run.py states 92 positions over 71 signatures (the
17 SeqSetGaps, the 33 one-argument Seq and SeqSet forms, 19 of
appendInstantTransition and the 2 raquetRead), every value the one its wrapper passes; the 3 left
(raquet, clip, reclass) fill a NULL argument through statements the rules do not read; every other
key of every function equals that of master's parser. The suite passes 525 tests with none
skipped, among them the two of tests/test_boundargs.py NullDefaultBindTests.

Why: a call leaving an argument to its default answers as PostgreSQL does only when the binding
passes what the wrapper passes, and that value is the catalog's to state.