Slightly fewer allocations in npc::process_turn

Makes `has_bodypart_with_flag` slightly faster, about 5% better turn
performance.

The method `Character::has_bodypart_with_flag` is called by
`Character::has_flag`, which in turn is called many times as part of
`npc::process_turn`. An example game was measured, which led to 57993
calls to `has_bodypart_with_flag` for 119 npc turns.

This commit changes the implementation in `has_bodypart_with_flag` to
use `Creature::get_body()` instead of `Creature::get_all_body_parts`,
which means that we can use the `bodypart` obj directly without going
through `get_part()` while iterating.

src/character.cpp

@@ -11729,11 +11729,11 @@ int Character::count_bionic_with_flag( const json_character_flag &flag ) const
 
 bool Character::has_bodypart_with_flag( const json_character_flag &flag ) const
 {
-    for( const bodypart_id &bp : get_all_body_parts() ) {
-        if( bp->has_flag( flag ) ) {
+    for( const std::pair<const bodypart_str_id, bodypart> &elem : get_body() ) {
+        if( elem.first->has_flag( flag ) ) {
             return true;
         }
-        if( get_part( bp )->has_conditional_flag( flag ) ) {
+        if( elem.second.has_conditional_flag( flag ) ) {
             return true;
         }
     }