ggml : move FP16 <-> FP32 code to ggml-impl.h (#3861)

* ggml : move FP16 <-> FP32 stuff to ggml-impl.h

ggml-ci

* tests : fix ARM build

* ggml : explicitly initialize deprecated type traits

* ggml : add math.h to ggml-impl.h

* ggml : remove duplicate static assert macros

* ggml : prefix lookup tables with ggml_

ggml-ci

* ggml-impl : move extern "C" to start of file

ggml-quants.h

@@ -1,22 +1,12 @@
 #pragma once
 
-// This is a private API for quantization and dequantization
-// Should not be used directly, use ggml.h instead
+#include "ggml-impl.h"
 
-#include "ggml.h"
+// GGML internal header
 
 #include <stdint.h>
-#include <assert.h>
 #include <stddef.h>
 
-#ifndef static_assert
-#if defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 201100L)
-#define static_assert(cond, msg) _Static_assert(cond, msg)
-#else
-#define static_assert(cond, msg) struct global_scope_noop_trick
-#endif
-#endif
-
 #define QK4_0 32
 typedef struct {
     ggml_fp16_t d;          // delta