Rename zero_realloc option "strict" to "alloc".

With realloc(ptr, 0) being UB per C23, the option name "strict" makes less sense
now.  Rename to "alloc" which describes the behavior.

test/unit/zero_realloc_alloc.c

@@ -0,0 +1,48 @@
+#include "test/jemalloc_test.h"
+
+static uint64_t
+allocated() {
+	if (!config_stats) {
+		return 0;
+	}
+	uint64_t allocated;
+	size_t sz = sizeof(allocated);
+	expect_d_eq(mallctl("thread.allocated", (void *)&allocated, &sz, NULL,
+	    0), 0, "Unexpected mallctl failure");
+	return allocated;
+}
+
+static uint64_t
+deallocated() {
+	if (!config_stats) {
+		return 0;
+	}
+	uint64_t deallocated;
+	size_t sz = sizeof(deallocated);
+	expect_d_eq(mallctl("thread.deallocated", (void *)&deallocated, &sz,
+	    NULL, 0), 0, "Unexpected mallctl failure");
+	return deallocated;
+}
+
+TEST_BEGIN(test_realloc_alloc) {
+	void *ptr = mallocx(1, 0);
+	expect_ptr_not_null(ptr, "Unexpected mallocx error");
+	uint64_t allocated_before = allocated();
+	uint64_t deallocated_before = deallocated();
+	ptr = realloc(ptr, 0);
+	uint64_t allocated_after = allocated();
+	uint64_t deallocated_after = deallocated();
+	if (config_stats) {
+		expect_u64_lt(allocated_before, allocated_after,
+		    "Unexpected stats change");
+		expect_u64_lt(deallocated_before, deallocated_after,
+		    "Unexpected stats change");
+	}
+	dallocx(ptr, 0);
+}
+TEST_END
+int
+main(void) {
+	return test(
+	    test_realloc_alloc);
+}