Add options flags to string setters

[jeromekelleher]

Closes #1979

The idea of this was to open the ground for #1977, but I'm having second thoughts now because the x_table_set_columns doesn't have an options value (which I forgot).

I guess we could add an option to tsk_x_table_init(table, options) which is like TSK_EXTERNAL_MEMORY or something, which flicks a switch were we store pointers in set_columns and set_metadata_schema, set_reference_sequence_data etc. So then, we don't need these options values.

I guess the alternative is to add options to all the x_tables_set_columns.

Any thoughts @benjeffery?

[jeromekelleher]

Ah, I'd forgotten about the update case where we want to pass ownership of a large string to the table. This is easy to do, and definitely requires the options flag, so it's a done-deal that we need this. I'll update later.

[benjeffery]

Adding options to x_tables_set_columns seems exactly the kind of thing we should be doing before 1.0, so makes sense to me.

[jeromekelleher]

I was thinking the same thing...

[jeromekelleher]

OK, I think this is ready to go - might was well get the messy stuff out of the way before starting on #2006.

[jeromekelleher]

Oops, needs a CHANGELOG entry...

[codecov]

Codecov Report

Merging #1990 (959a028) into main (97e9dad) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1990   +/-   ##
=======================================
  Coverage   93.35%   93.35%           
=======================================
  Files          27       27           
  Lines       25521    25522    +1     
  Branches     1111     1111           
=======================================
+ Hits        23826    23827    +1     
  Misses       1660     1660           
  Partials       35       35           

Flag	Coverage Δ
c-tests	92.37% <100.00%> (+<0.01%)	⬆️
lwt-tests	89.05% <100.00%> (ø)
python-c-tests	72.09% <100.00%> (ø)
python-tests	98.79% <ø> (ø)

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Impacted Files	Coverage Δ
c/tskit/tables.c	90.26% <100.00%> (+<0.01%)	⬆️
python/_tskitmodule.c	90.94% <100.00%> (ø)
python/lwt_interface/tskit_lwt_interface.h	90.81% <100.00%> (ø)

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[jeromekelleher]

Ugh, maybe we don't want to do this. As noted in #2006 (comment) we'll have to drop all the const qualifiers in the signatures if we do it this way, which is particularly annoying when dealing with literal strings.

Maybe we should have a separate set of methods instead?

[jeromekelleher]

Closed in favour of "takeset" methods, #2016