refactor: run IWYU on entire repo

Reference: https://github.com/neovim/neovim/issues/6371.

src/nvim/mapping.h

@@ -13,6 +13,10 @@
 #include "nvim/regexp_defs.h"  // IWYU pragma: keep
 #include "nvim/types_defs.h"  // IWYU pragma: keep
 
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "mapping.h.generated.h"
+#endif
+
 /// Used for the first argument of do_map()
 enum {
   MAPTYPE_MAP     = 0,
@@ -20,6 +24,23 @@ enum {
   MAPTYPE_NOREMAP = 2,
 };
 
-#ifdef INCLUDE_GENERATED_DECLARATIONS
-# include "mapping.h.generated.h"
-#endif
+/// Adjust chars in a language according to 'langmap' option.
+/// NOTE that there is no noticeable overhead if 'langmap' is not set.
+/// When set the overhead for characters < 256 is small.
+/// Don't apply 'langmap' if the character comes from the Stuff buffer or from a
+/// mapping and the langnoremap option was set.
+/// The do-while is just to ignore a ';' after the macro.
+#define LANGMAP_ADJUST(c, condition) \
+  do { \
+    if (*p_langmap \
+        && (condition) \
+        && (p_lrm || (vgetc_busy ? typebuf_maplen() == 0 : KeyTyped)) \
+        && !KeyStuffed \
+        && (c) >= 0) \
+    { \
+      if ((c) < 256) \
+      c = langmap_mapchar[c]; \
+      else \
+      c = langmap_adjust_mb(c); \
+    } \
+  } while (0)