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/ex_cmds2.h

@@ -1,6 +1,8 @@
 #ifndef NVIM_EX_CMDS2_H
 #define NVIM_EX_CMDS2_H
 
+#include <stdbool.h>
+
 #include "nvim/ex_docmd.h"
 
 typedef void (*DoInRuntimepathCB)(char_u *, void *);

src/nvim/message.h

@@ -1,6 +1,8 @@
 #ifndef NVIM_MESSAGE_H
 #define NVIM_MESSAGE_H
 
+#include <stdbool.h>
+
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "message.h.generated.h"
 #endif

src/nvim/ops.h

@@ -1,6 +1,8 @@
 #ifndef NVIM_OPS_H
 #define NVIM_OPS_H
 
+#include <stdbool.h>
+
 #include "nvim/types.h"
 
 typedef int (*Indenter)(void);

src/nvim/os/channel.h

@@ -1,6 +1,7 @@
 #ifndef NVIM_OS_CHANNEL_H
 #define NVIM_OS_CHANNEL_H
 
+#include <stdbool.h>
 #include <uv.h>
 
 #include "nvim/api/private/defs.h"

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"

src/nvim/screen.h

@@ -1,6 +1,8 @@
 #ifndef NVIM_SCREEN_H
 #define NVIM_SCREEN_H
 
+#include <stdbool.h>
+
 /*
  * flags for update_screen()
  * The higher the value, the higher the priority

src/nvim/strings.h

@@ -1,6 +1,8 @@
 #ifndef NVIM_STRINGS_H
 #define NVIM_STRINGS_H
 
+#include <stdbool.h>
+
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "strings.h.generated.h"
 #endif