Convert tsqueryin and tsvectorin to report errors softly.

Convert tsqueryin and tsvectorin to report errors softly.

This is slightly tedious because the adjustments cascade through
a couple of levels of subroutines, but it's not very hard.
I chose to avoid changing function signatures more than absolutely
necessary, by passing the escontext pointer in existing structs
where possible.

tsquery's nuisance NOTICEs about empty queries are suppressed in
soft-error mode, since they're not errors and we surely don't want
them to be shown to the user anyway.  Maybe that whole behavior
should be reconsidered.

Discussion: https://postgr.es/m/3824377.1672076822@sss.pgh.pa.us