libc: Implement bsearch_s(), document bsearch_b(), and add unit tests

- Implement bsearch_s() as per §K.3.6.3.2 in C23, first specified
  in C11.  It behaves identically to bsearch(), except the callback
  is called with a third argument, context, which is passed through
  from the caller, and it also performs runtime constraint checking
  on its arguments.
- Document bsearch_b(), bsearch_s(), and add history section
- Add rudimentary unit tests for bsearch(), bsearch_b(), and bsearch_s()

Reviewed by:	dteske, fuz
Approved by:    dteske (mentor), fuz (mentor)
MFC after:	1 month
Differential Revision:	https://reviews.freebsd.org/D58876

include/stdlib.h

@@ -411,6 +411,9 @@ _Noreturn void abort_handler_s(const char * __restrict, void * __restrict,
 /* K3.6.1.3 */
 void ignore_handler_s(const char * __restrict, void * __restrict, errno_t);
 /* K.3.6.3.2 */
+void	*bsearch_s(const void *, const void *, rsize_t, rsize_t,
+    int (*)(const void *, const void *, void *), void *);
+/* K.3.6.3.3 */
 errno_t	 qsort_s(void *, rsize_t, rsize_t,
     int (*)(const void *, const void *, void *), void *);
 #endif /* __EXT1_VISIBLE */
@@ -428,6 +431,13 @@ __NULLABILITY_PRAGMA_POP
 	(const void *)(bsearch_b)((key), (base), (nmemb), (size), (compar)), \
 	(bsearch_b)((key), (base), (nmemb), (size), (compar)))
 #endif
+#if __EXT1_VISIBLE
+#define	bsearch_s(key, base, nmemb, size, compar, context)		\
+	__qualsel((base),						\
+	(const void *)(bsearch_s)((key), (base), (nmemb), (size),	\
+	    (compar), (context)),					\
+	(bsearch_s)((key), (base), (nmemb), (size), (compar), (context)))
+#endif
 #endif
 
 #endif /* !_STDLIB_H_ */