patch 8.2.4650: "import autoload" only works with using 'runtimepath'

Problem:    "import autoload" only works with using 'runtimepath'.
Solution:   Also support a relative and absolute file name.
diff --git a/src/structs.h b/src/structs.h
index 36eb054..737b9f9 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1833,7 +1833,7 @@
  */
 typedef struct
 {
-    char_u	*sn_name;
+    char_u	*sn_name;	    // full path of script file
     int		sn_script_seq;	    // latest sctx_T sc_seq value
 
     // "sn_vars" stores the s: variables currently valid.  When leaving a block
@@ -1864,9 +1864,12 @@
     char_u	*sn_save_cpo;	// 'cpo' value when :vim9script found
     char	sn_is_vimrc;	// .vimrc file, do not restore 'cpo'
 
-    // for "vim9script autoload" this is "dir#scriptname#"
+    // for a Vim9 script under "rtp/autoload/" this is "dir#scriptname#"
     char_u	*sn_autoload_prefix;
 
+    // TRUE for a script used with "import autoload './dirname/script.vim'"
+    int		sn_import_autoload;
+
 # ifdef FEAT_PROFILE
     int		sn_prof_on;	// TRUE when script is/was profiled
     int		sn_pr_force;	// forceit: profile functions in this script