Fix some `FT_Fixed` vs. `FT_Long` confusion.

`FT_Fixed` and `FT_Long` are both typedef'ed to be `signed long`.  However,
`FT_Fixed` implies that the lower 16 bits are being used to express
fractional values and so these two types should not be confused.

* include/freetype/internal/services/svmm.h (FT_Set_MM_Blend_Func): Use
`FT_Fixed` for `coords`.  Users are passing `FT_Fixed` and implementations
are taking `FT_Fixed`.
(FT_Get_MM_Blend_Func): Ditto.

* src/autofit/afcjk.c (af_cjk_metrics_check_digits): Use `FT_Long` for
`advance` and `old_advance`.  `advance`'s address is passed as `FT_Long*` to
`af_shaper_get_elem`, which writes the advance in em units (not fixed).  The
exact value is not important here as it is only compared to check whether it
has changed.

* src/autofit/aflatin.c (af_latin_metrics_check_digits): Ditto.

include/freetype/internal/services/svmm.h

@@ -60,9 +60,9 @@ FT_BEGIN_HEADER
   /* use return value -1 to indicate that the new coordinates  */
   /* are equal to the current ones; no changes are thus needed */
   typedef FT_Error
-  (*FT_Set_MM_Blend_Func)( FT_Face   face,
-                           FT_UInt   num_coords,
-                           FT_Long*  coords );
+  (*FT_Set_MM_Blend_Func)( FT_Face    face,
+                           FT_UInt    num_coords,
+                           FT_Fixed*  coords );
 
   typedef FT_Error
   (*FT_Get_Var_Design_Func)( FT_Face    face,
@@ -78,9 +78,9 @@ FT_BEGIN_HEADER
                                          FT_UInt  *instance_index );
 
   typedef FT_Error
-  (*FT_Get_MM_Blend_Func)( FT_Face   face,
-                           FT_UInt   num_coords,
-                           FT_Long*  coords );
+  (*FT_Get_MM_Blend_Func)( FT_Face    face,
+                           FT_UInt    num_coords,
+                           FT_Fixed*  coords );
 
   typedef FT_Error
   (*FT_Get_Var_Blend_Func)( FT_Face      face,

src/autofit/afcjk.c

@@ -567,8 +567,8 @@
   af_cjk_metrics_check_digits( AF_CJKMetrics  metrics,
                                FT_Face        face )
   {
-    FT_Bool   started = 0, same_width = 1;
-    FT_Fixed  advance = 0, old_advance = 0;
+    FT_Bool  started = 0, same_width = 1;
+    FT_Long  advance = 0, old_advance = 0;
 
     /* If HarfBuzz is not available, we need a pointer to a single */
     /* unsigned long value.                                        */

src/autofit/aflatin.c

@@ -1065,8 +1065,8 @@
   af_latin_metrics_check_digits( AF_LatinMetrics  metrics,
                                  FT_Face          face )
   {
-    FT_Bool   started = 0, same_width = 1;
-    FT_Fixed  advance = 0, old_advance = 0;
+    FT_Bool  started = 0, same_width = 1;
+    FT_Long  advance = 0, old_advance = 0;
 
     /* If HarfBuzz is not available, we need a pointer to a single */
     /* unsigned long value.                                        */