refactor(map): avoid duplicated khash_t types for values

This reduces the total number of khash_t instantiations from 22 to 8.

Make the khash internal functions take the size of values as a runtime
parameter. This is abstracted with typesafe Map containers which
are still specialized for both key, value type.

Introduce `Set(key)` type for when there is no value.

Refactor shada.c to use Map/Set instead of khash directly.
This requires `map_ref` operation to be more flexible.
Return pointers to both key and value, plus an indicator for new_item.
As a bonus, `map_key` is now redundant.

Instead of Map(cstr_t, FileMarks), use a pointer map as the FileMarks struct is
humongous.

Make `event_strings` actually work like an intern pool instead of wtf it
was doing before.

src/nvim/lua/executor.c

@@ -910,7 +910,7 @@ static void nlua_common_free_all_mem(lua_State *lstate)
   if (nlua_track_refs) {
     // in case there are leaked luarefs, leak the associated memory
     // to get LeakSanitizer stacktraces on exit
-    pmap_destroy(handle_T)(&ref_state->ref_markers);
+    map_destroy(int, &ref_state->ref_markers);
   }
 #endif
 
@@ -1285,7 +1285,7 @@ LuaRef nlua_ref(lua_State *lstate, nlua_ref_state_t *ref_state, int index)
 #ifdef NLUA_TRACK_REFS
     if (nlua_track_refs) {
       // dummy allocation to make LeakSanitizer track our luarefs
-      pmap_put(handle_T)(&ref_state->ref_markers, ref, xmalloc(3));
+      pmap_put(int)(&ref_state->ref_markers, ref, xmalloc(3));
     }
 #endif
   }
@@ -1305,7 +1305,7 @@ void nlua_unref(lua_State *lstate, nlua_ref_state_t *ref_state, LuaRef ref)
 #ifdef NLUA_TRACK_REFS
     // NB: don't remove entry from map to track double-unref
     if (nlua_track_refs) {
-      xfree(pmap_get(handle_T)(&ref_state->ref_markers, ref));
+      xfree(pmap_get(int)(&ref_state->ref_markers, ref));
     }
 #endif
     luaL_unref(lstate, LUA_REGISTRYINDEX, ref);

src/nvim/lua/executor.h

@@ -24,7 +24,7 @@ typedef struct {
   LuaRef empty_dict_ref;
   int ref_count;
 #if __has_feature(address_sanitizer)
-  PMap(handle_T) ref_markers;
+  PMap(int) ref_markers;
 #endif
 } nlua_ref_state_t;
 

src/nvim/lua/treesitter.c

@@ -231,9 +231,9 @@ int tslua_remove_lang(lua_State *L)
   const char *lang_name = luaL_checkstring(L, 1);
   bool present = pmap_has(cstr_t)(&langs, lang_name);
   if (present) {
-    char *key = (char *)pmap_key(cstr_t)(&langs, lang_name);
-    pmap_del(cstr_t)(&langs, lang_name);
-    xfree(key);
+    cstr_t key;
+    pmap_del(cstr_t)(&langs, lang_name, &key);
+    xfree((void *)key);
   }
   lua_pushboolean(L, present);
   return 1;