fix(highlight): add force in nvim_set_hl

src/nvim/api/keysets.h

@@ -168,6 +168,7 @@ typedef struct {
   Integer blend;
   Boolean fg_indexed;
   Boolean bg_indexed;
+  Boolean force;
 } Dict(highlight);
 
 typedef struct {

src/nvim/api/vim.c

@@ -151,6 +151,7 @@ Dictionary nvim_get_hl(Integer ns_id, Dict(get_highlight) *opts, Arena *arena, E
 ///                - cterm: cterm attribute map, like |highlight-args|. If not set,
 ///                         cterm attributes will match those from the attribute map
 ///                         documented above.
+///                - force: if true force update the highlight group when it exists.
 /// @param[out] err Error details, if any
 ///
 // TODO(bfredl): val should take update vs reset flag