string-table: Introduce DECLARE_STRING_TABLE_LOOKUP() and friends

Let's introduce these for the following two reasons:
- Using them makes sure the parameter names match between declaration
  and definition (if both use the corresponding macros).
- They make sure developers can't forget the _const_ and _pure_
  attributes for the declarations.

This commit also includes some include sorting fixes

src/basic/log.h

@@ -40,8 +40,7 @@ static inline void clear_log_syntax_callback(dummy_t *dummy) {
           set_log_syntax_callback(/* cb= */ NULL, /* userdata= */ NULL);
 }
 
-const char* log_target_to_string(LogTarget target) _const_;
-LogTarget log_target_from_string(const char *s) _pure_;
+DECLARE_STRING_TABLE_LOOKUP(log_target, LogTarget);
 void log_set_target(LogTarget target);
 void log_set_target_and_open(LogTarget target);
 int log_set_target_from_string(const char *e);