allocf.c: rename mrb_default_alloc to mrb_basic_alloc_func

Along with removing mrb_state first argument from the function. From
mruby 3.2, this function is *not* the default function, but the entry
point that can be redefined for the application. The function in
`src/allocf.c` is the default *implementation* (using malloc / realloc /
free) of the function.

src/allocf.c

@@ -8,14 +8,13 @@
 
 /* This function serves as the default memory allocation function and accepts four arguments:
  *
- * - `mrb`: An instance of `mrb_state`. It's important to note that for the initial allocation (used to allocate the `mrb_state` itself), `mrb` is set to NULL.
  * - `p`: The previous pointer to the memory region. For memory allocation, this parameter is NULL.
  * - `size`: The new size of the memory region to be returned.
  * - `ud`: User data, represented as a `void*`, which is passed to the `mrb_state`.
  */
 
 void*
-mrb_default_allocf(mrb_state *mrb, void *p, size_t size, void *ud)
+mrb_basic_alloc_func(void *p, size_t size, void *ud)
 {
   if (size == 0) {
     /* `free(NULL)` should be no-op */

src/gc.c

@@ -194,10 +194,10 @@ mrb_realloc_simple(mrb_state *mrb, void *p,  size_t len)
     mrb_full_gc(mrb);
   }
 #endif
-  p2 = mrb_default_allocf(mrb, p, len, NULL);
+  p2 = mrb_basic_alloc_func(p, len, NULL);
   if (!p2 && len > 0 && mrb->gc.heaps && mrb->gc.state != MRB_GC_STATE_SWEEP) {
     mrb_full_gc(mrb);
-    p2 = mrb_default_allocf(mrb, p, len, NULL);
+    p2 = mrb_basic_alloc_func(p, len, NULL);
   }
 
   return p2;
@@ -256,7 +256,7 @@ mrb_calloc(mrb_state *mrb, size_t nelem, size_t len)
 MRB_API void
 mrb_free(mrb_state *mrb, void *p)
 {
-  mrb_default_allocf(mrb, p, 0, NULL);
+  mrb_basic_alloc_func(p, 0, NULL);
 }
 
 MRB_API void*

src/state.c

@@ -41,8 +41,8 @@ mrb_open_core(mrb_allocf f, void *ud)
   static const mrb_state mrb_state_zero = { 0 };
   mrb_state *mrb;
 
-  if (f == NULL) f = mrb_default_allocf;
-  mrb = (mrb_state*)(f)(NULL, NULL, sizeof(mrb_state), ud);
+  if (f == NULL) f = mrb_basic_alloc_func;
+  mrb = (mrb_state*)(f)(NULL, sizeof(mrb_state), ud);
   if (mrb == NULL) return NULL;
 
   *mrb = mrb_state_zero;
@@ -59,7 +59,7 @@ mrb_open_core(mrb_allocf f, void *ud)
 MRB_API mrb_state*
 mrb_open(void)
 {
-  mrb_state *mrb = mrb_open_allocf(mrb_default_allocf, NULL);
+  mrb_state *mrb = mrb_open_allocf(mrb_basic_alloc_func, NULL);
 
   return mrb;
 }