Add handler functions for Datum/Bools arrays

[fabriziomello]

When updating catalog tables we rely on low level functions instead of SQL statements and in order to read/write data from/to those tables we frequent do something like:

Datum values[natts] = { 0 };
bool nulls[natts] = { false };
char *char_value = "foo";

if (char_value != NULL)
    values[AttrNumberGetAttrOffset(text_value_offset)] =
        PointerGetDatum(cstring_to_text(char_value);
else
    null[AttrNumberGetAttrOffset(char_value_offset)] = true;

So instead of using a pair of Datum and bool arrays we'll replace it by using arrays of NullableDatum that contains both members and introduce some accessor functions to encapsulate the logic to fill the proper values, like:

ts_datum_set_text(int index, NullableDatum *datums, text *value);
ts_datum_set_bool(int index, NullableDatum *datums, bool value);

We also introduce a new ts_heap_form_tuple that essentially to the same as Postgres heap_form_tuple but using array of NullableDatum instead of Datum and bool arrays.

In this first commit we added only the necessary accessor functions to refactor the existing create_cagg_validate_query_datum as example. More accessor functions to deal with other C types should be introduced in the future.

Disable-check: force-changelog-file

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 80.99%. Comparing base (59f50f2) to head (d691e02).
Report is 59 commits behind head on main.

Files	Patch %	Lines
src/utils.h	50.00%	0 Missing and 4 partials ⚠️
tsl/src/continuous_aggs/utils.c	92.85%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6735      +/-   ##
==========================================
+ Coverage   80.06%   80.99%   +0.92%     
==========================================
  Files         190      191       +1     
  Lines       37181    36351     -830     
  Branches     9450     9435      -15     
==========================================
- Hits        29770    29443     -327     
- Misses       2997     3159     +162     
+ Partials     4414     3749     -665     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.