patch 9.2.0365: using int as bool

Problem:  using int as bool
Solution: refactor: use bool type for internal flags in buf_T
          (Hirohito Higashi)

Change the type of 23 internal state flag fields in buf_T from int
to bool for improved type clarity and code readability.

These fields are pure boolean flags that are never accessed via the
option system's varp (which uses *(int *)varp = value), never compared
with int fields holding non-0/1 values, and never use tristate values.

Converted fields:
- State flags: b_dev_valid, b_saving, b_mod_set, b_new_change,
  b_marks_read, b_modified_was_set, b_did_filetype, b_keep_filetype,
  b_au_did_filetype, b_u_synced, b_scanned, b_p_initialized
- Characteristic flags: b_has_textprop, b_may_swap, b_did_warn,
  b_help, b_spell, b_shortname, b_has_sign_column, b_netbeans_file,
  b_was_netbeans_file, b_write_to_channel, b_diff_failed

All TRUE/FALSE assignments to these fields have been updated to
true/false accordingly. The type of temporary save variables
(e.g. help_save in tag.c) has also been adjusted to bool.

Option value fields (b_p_XXX) are kept as int because they are
accessed via the option system and some use tristate (-1) semantics.
Fields compared with int option values (b_start_eof, b_start_eol,
b_start_bomb) are also kept as int to preserve comparison integrity.

closes: #20020

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Signed-off-by: Hirohito Higashi <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/bufwrite.c

@@ -1160,7 +1160,7 @@ buf_write(
     got_int = FALSE;
 
     // Mark the buffer as 'being saved' to prevent changed buffer warnings
-    buf->b_saving = TRUE;
+    buf->b_saving = true;
 
     // If we are not appending or filtering, the file exists, and the
     // 'writebackup', 'backup' or 'patchmode' option is set, need a backup.
@@ -1407,13 +1407,13 @@ buf_write(
 			    // may try again with 'shortname' set
 			    if (!(buf->b_shortname || buf->b_p_sn))
 			    {
-				buf->b_shortname = TRUE;
+				buf->b_shortname = true;
 				did_set_shortname = TRUE;
 				continue;
 			    }
 				// setting shortname didn't help
 			    if (did_set_shortname)
-				buf->b_shortname = FALSE;
+				buf->b_shortname = false;
 			    break;
 			}
 #endif
@@ -2543,7 +2543,7 @@ fail:
 nofail:
 
     // Done saving, we accept changed buffer warnings again
-    buf->b_saving = FALSE;
+    buf->b_saving = false;
 
     vim_free(backup);
     if (buffer != smallbuf)
@@ -2661,7 +2661,7 @@ nofail:
 #ifdef FEAT_VIMINFO
     // Make sure marks will be written out to the viminfo file later, even when
     // the file is new.
-    curbuf->b_marks_read = TRUE;
+    curbuf->b_marks_read = true;
 #endif
 
     got_int |= prev_got_int;