fix iseq kwargs table and original_iseq leaks

[HParker]

bug: https://bugs.ruby-lang.org/issues/19903

Reproduction:

10.times do
  100_000.times do
    RubyVM::InstructionSequence.load_from_binary(RubyVM::InstructionSequence.compile("def foo(bar:); end; foo(bar: :baz)").to_binary)
  end
  puts `ps -o rss= -p #{$$}`
end

before:

39636
60756
82140
103260
124380
145764
166884
188004
209388
230508

after:

25184
31784
38648
45248
51848
58712
65312
71912
78776
85376

Valgrind:

==62738== 496 bytes in 38 blocks are definitely lost in loss record 1 of 1
==62738==    at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==62738==    by 0x16F754: objspace_xmalloc0 (gc.c:12352)
==62738==    by 0x16FB5C: ruby_xmalloc2_body (gc.c:12599)
==62738==    by 0x173599: ruby_xmalloc2 (gc.c:14166)
==62738==    by 0x41D022: ibf_load_alloc (compile.c:11188)
==62738==    by 0x41E6BF: ibf_load_param_keyword (compile.c:11692)
==62738==    by 0x42098F: ibf_load_iseq_each (compile.c:12316)
==62738==    by 0x422A6F: rb_ibf_load_iseq_complete (compile.c:13183)
==62738==    by 0x422B59: ibf_load_iseq (compile.c:13238)
==62738==    by 0x41DD31: ibf_load_code (compile.c:11542)
==62738==    by 0x420AF5: ibf_load_iseq_each (compile.c:12326)
==62738==    by 0x422A6F: rb_ibf_load_iseq_complete (compile.c:13183)

==94377== 48 bytes in 1 blocks are definitely lost in loss record 1 of 1
==94377==    at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==94377==    by 0x16F754: objspace_xmalloc0 (gc.c:12352)
==94377==    by 0x16FB5C: ruby_xmalloc2_body (gc.c:12599)
==94377==    by 0x173599: ruby_xmalloc2 (gc.c:14166)
==94377==    by 0x3EFC5A: ISEQ_ORIGINAL_ISEQ_ALLOC (iseq.h:77)
==94377==    by 0x3F6B50: rb_iseq_original_iseq (compile.c:923)
==94377==    by 0x41D6C7: ibf_dump_code (compile.c:11404)
==94377==    by 0x41F7DF: ibf_dump_iseq_each (compile.c:12027)
==94377==    by 0x420C3E: ibf_dump_iseq_list_i (compile.c:12361)
==94377==    by 0x2BDEF8: apply_functor (st.c:1617)
==94377==    by 0x2BDB5B: st_general_foreach (st.c:1527)
==94377==    by 0x2BDF56: rb_st_foreach (st.c:1624)

This improves memory handling and reduces memory growth over time.
I didn't add a leak test because I can't reproduce this issue before the test times out.

[peterzhu2118]

Minor nit, otherwise looks good!

[peterzhu2118]

ruby_xfree can handle NULL values, so we don't need to explicitly check that here.

Suggested change

	if (body->variable.original_iseq != NULL)
	ruby_xfree(body->variable.original_iseq);
	ruby_xfree(body->variable.original_iseq);