Include stdbool.h in headers which have functions with bool in signature

Done by manual inspecting of the output of this script:
grep -r -l -w "bool" * | grep 'c$' | sed 's/.c$//' > has_bool
grep -r -l -w "stdbool.h" * | grep 'h$' | sed 's/.h$//' > has_include
grep -F -x -v -f has_include has_bool

src/nvim/os/os.h

@@ -1,5 +1,7 @@
 #ifndef NVIM_OS_OS_H
 #define NVIM_OS_OS_H
+
+#include <stdbool.h>
 #include <uv.h>
 
 #include "nvim/os/fs_defs.h"