patch 9.1.0568: Cannot expand paths from 'cdpath' setting

Problem:  Cannot expand paths from 'cdpath' setting
          (Daniel Hahler)
Solution: Implement 'cdpath' completion, add the new 'dir_in_path'
          completion type (LemonBoy)

fixes #374
closes: #15205

Signed-off-by: LemonBoy <thatlemon@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/vim.h b/src/vim.h
index a359162..c022f2e 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -843,6 +843,8 @@
 #define EXPAND_ARGOPT		56
 #define EXPAND_TERMINALOPT	57
 #define EXPAND_KEYMAP		58
+#define EXPAND_DIRS_IN_CDPATH	59
+
 
 // Values for exmode_active (0 is no exmode)
 #define EXMODE_NORMAL		1
@@ -898,6 +900,7 @@
 #define EW_DODOT	0x4000	// also files starting with a dot
 #define EW_EMPTYOK	0x8000	// no matches is not an error
 #define EW_NOTENV	0x10000	// do not expand environment variables
+#define EW_CDPATH	0x20000	// search in 'cdpath' too
 
 // Flags for find_file_*() functions.
 #define FINDFILE_FILE	0	// only files