ota: Import One True Awk from 20231102 (254b979f32df)

This is a rollup of a lot of changes. In summary, lots of bug fixes,
Unicode support and CSV support to match the 2nd Edition of the Awk
Book.

In detail, from AWK's FIXES and FIXES.1e:

From FIXES:
Oct 30, 2023:
multiple fixes and a minor code cleanup.
disabled utf-8 for non-multibyte locales, such as C or POSIX.
fixed a bad char * cast that causes incorrect results on big-endian
systems. also fixed an out-of-bounds read for empty CCL.
fixed a buffer overflow in substr with utf-8 strings.
many thanks to Todd C Miller.

Sep 24, 2023:
fnematch and getrune have been overhauled to solve issues around
unicode FS and RS. also fixed gsub null match issue with unicode.
big thanks to Arnold Robbins.

Sep 12, 2023:
Fixed a length error in u8_byte2char that set RSTART to
incorrect (cannot happen) value for EOL match(str, /$/).

[This entry is a summary, not a precise list of changes.]

Added --csv option to enable processing of comma-separated
values inputs. When --csv is enabled, fields are separated
by commas, fields may be quoted with " double quotes, fields
may contain embedded newlines.

If no explicit separator argument is provided, split() uses
the setting of --csv to determine how fields are split.

Strings may now contain UTF-8 code points (not necessarily
characters). Functions that operate on characters, like
length, substr, index, match, etc., use UTF-8, so the length
of a string of 3 emojis is 3, not 12 as it would be if bytes
were counted.

Regular expressions are processes as UTF-8.

Unicode literals can be written as \u followed by one
to eight hexadecimal digits. These may appear in strings and
regular expressions.

From FIXES.1e:

Sep 06, 2023:
Fix edge case where FS is changed on commandline. Thanks to
Gordon Shephard and Miguel Pineiro Jr.

Fix regular expression clobbering in the lexer, where lexer does
not make a copy of regexp literals. also makedfa memory leaks have
been plugged. Thanks to Miguel Pineiro Jr.

Dec 15, 2022:
Force hex escapes in strings to be no more than two characters,
as they already are in regular expressions. This brings internal
consistency, as well as consistency with gawk. Thanks to
Arnold Robbins.

Sep 12, 2022:
adjbuf minlen error (cannot be 0) in cat, resulting in NULL pbuf.
discovered by todd miller. also use-after-free issue with
tempfree in cat, thanks to Miguel Pineiro Jr and valgrind.

Aug 30, 2022:
Various leaks and use-after-free issues plugged/fixed.
Thanks to Miguel Pineiro Jr. <mpj@pineiro.cc>.

May 23, 2022:
Memory leak when assigning a string to some of the built-in
variables. allocated string erroneously marked DONTFREE.
Thanks to Miguel Pineiro Jr. <mpj@pineiro.cc>.

Mar 14, 2022:
Historic bug: command-line "name=value" assignment had been
truncating its entry in ARGV. (circa 1989) Thanks to
Miguel Pineiro Jr. <mpj@pineiro.cc>.

Mar 3, 2022:
Fixed file management memory leak that appears to have been
there since the files array was first initialized with stdin,
stdout, and stderr (circa 1992). Thanks to Miguel Pineiro Jr.
<mpj@pineiro.cc>.

December 8, 2021:
The error handling in closefile and closeall was mangled. Long
standing warnings had been made fatal and some fatal errors went
undetected. Thanks to Miguel Pineiro Jr. <mpj@pineiro.cc>.

Nov 03, 2021:

getline accesses uninitialized data after getrec()

returns 0 on EOF and leaves the contents of buf unchanged.
Thanks to Volodymyr Gubarkov, and Todd C Miller.

Oct 12, 2021:
The fix for #83 changed the code to insert 2 chars, but the
call to adjbuf just above it only allows for 1 char. This can
cause a heap buffer overflow.

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