memory: Add free wrapper and refactor project to use it

We already use wrappers for allocation, the new `xfree` function is the
equivalent for deallocation and provides a way to fully replace the malloc
implementation used by Neovim.

src/nvim/api/buffer.c

@@ -58,7 +58,7 @@ String buffer_get_line(Buffer buffer, Integer index, Error *err)
     rv = slice.items[0].data.string;
   }
 
-  free(slice.items);
+  xfree(slice.items);
 
   return rv;
 }
@@ -144,10 +144,10 @@ ArrayOf(String) buffer_get_line_slice(Buffer buffer,
 end:
   if (err->set) {
     for (size_t i = 0; i < rv.size; i++) {
-      free(rv.items[i].data.string.data);
+      xfree(rv.items[i].data.string.data);
     }
 
-    free(rv.items);
+    xfree(rv.items);
     rv.items = NULL;
   }
 
@@ -280,7 +280,7 @@ void buffer_set_line_slice(Buffer buffer,
     }
 
     // Same as with replacing, but we also need to free lines
-    free(lines[i]);
+    xfree(lines[i]);
     lines[i] = NULL;
     extra++;
   }
@@ -301,10 +301,10 @@ void buffer_set_line_slice(Buffer buffer,
 
 end:
   for (size_t i = 0; i < new_len; i++) {
-    free(lines[i]);
+    xfree(lines[i]);
   }
 
-  free(lines);
+  xfree(lines);
   restore_win_for_buf(save_curwin, save_curtab, save_curbuf);
   try_end(err);
 }

src/nvim/api/private/helpers.c

@@ -61,7 +61,7 @@ bool try_end(Error *err)
     free_global_msglist();
 
     if (should_free) {
-      free(msg);
+      xfree(msg);
     }
   } else if (did_throw) {
     api_set_error(err, Exception, "%s", current_exception->value);
@@ -489,7 +489,7 @@ void api_free_string(String value)
     return;
   }
 
-  free(value.data);
+  xfree(value.data);
 }
 
 void api_free_object(Object value)
@@ -527,7 +527,7 @@ void api_free_array(Array value)
     api_free_object(value.items[i]);
   }
 
-  free(value.items);
+  xfree(value.items);
 }
 
 void api_free_dictionary(Dictionary value)
@@ -537,7 +537,7 @@ void api_free_dictionary(Dictionary value)
     api_free_object(value.items[i].value);
   }
 
-  free(value.items);
+  xfree(value.items);
 }
 
 Dictionary api_metadata(void)

src/nvim/api/vim.c

@@ -85,7 +85,7 @@ void vim_feedkeys(String keys, String mode, Boolean escape_csi)
       insert ? 0 : typebuf.tb_len, !typed, false);
 
   if (escape_csi) {
-      free(keys_esc);
+      xfree(keys_esc);
   }
 
   if (vgetc_busy)