Avoid crashes when casifying noncontiguous regions

This is a followon fix for Bug#37477.
* lisp/simple.el (region-extract-function):
Use setq here, since the var is now defined in C code.
* src/casefiddle.c (casify_pnc_region): New function.
(Fupcase_region, Fdowncase_region, Fcapitalize_region)
(Fupcase_initials_region): Use it.
(Fupcase_initials_region): Add region-noncontiguous-p flag
for consistency with the others.  All uses changed.
(syms_of_casefiddle): Define Qbounds, Vregion_extract_function.
* src/insdel.c (prepare_to_modify_buffer_1):
* src/keyboard.c (command_loop_1):
Use Vregion_extraction_function.
* src/insdel.c (syms_of_insdel): No need to define
* test/src/casefiddle-tests.el (casefiddle-oldfunc): New var.
(casefiddle-loopfunc, casefiddle-badfunc): New functions.
(casefiddle-invalid-region-extract-function): New test.
1 job for master in 54 minutes and 14 seconds (queued for 3 seconds)
Status Job ID Name Coverage
failed #3416


Name Stage Failure
test-all Test
Makefile:319: recipe for target 'check-doit' failed
make[2]: Leaving directory '/builds/emacs/emacs/test'
make[2]: *** [check-doit] Error 1
Makefile:294: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:959: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1