patch 8.2.1376: Vim9: expression mapping causes error for using :import

Problem:    Vim9: expression mapping causes error for using :import.
Solution:   Add EX_LOCK_OK to :import and :export. (closes 3606)

Author: brammool

src/ex_cmds.h

@@ -572,7 +572,7 @@ EXCMD(CMD_exit,		"exit",		ex_exit,
 	EX_RANGE|EX_WHOLEFOLD|EX_BANG|EX_FILE1|EX_ARGOPT|EX_DFLALL|EX_TRLBAR|EX_CMDWIN|EX_LOCK_OK,
 	ADDR_LINES),
 EXCMD(CMD_export,	"export",	ex_export,
-	EX_EXTRA|EX_NOTRLCOM,
+	EX_EXTRA|EX_NOTRLCOM|EX_LOCK_OK,
 	ADDR_NONE),
 EXCMD(CMD_exusage,	"exusage",	ex_exusage,
 	EX_TRLBAR,
@@ -698,7 +698,7 @@ EXCMD(CMD_imenu,	"imenu",	ex_menu,
 	EX_RANGE|EX_ZEROR|EX_EXTRA|EX_TRLBAR|EX_NOTRLCOM|EX_CTRLV|EX_CMDWIN|EX_LOCK_OK,
 	ADDR_OTHER),
 EXCMD(CMD_import,	"import",	ex_import,
-	EX_EXTRA|EX_NOTRLCOM,
+	EX_EXTRA|EX_NOTRLCOM|EX_LOCK_OK,
 	ADDR_NONE),
 EXCMD(CMD_inoremap,	"inoremap",	ex_map,
 	EX_EXTRA|EX_TRLBAR|EX_NOTRLCOM|EX_CTRLV|EX_CMDWIN|EX_LOCK_OK,

src/testdir/test_vim9_script.vim

@@ -1351,6 +1351,36 @@ def Test_vim9_import_export()
   delete('Xvim9_script')
 enddef
 
+func g:Trigger()
+  source Ximport.vim
+  return "echo 'yes'\<CR>"
+endfunc
+
+def Test_import_export_expr_map()
+  # check that :import and :export work when buffer is locked
+  let export_lines =<< trim END
+    vim9script
+    export def That(): string
+      return 'yes'
+    enddef
+  END
+  writefile(export_lines, 'Xexport_that.vim')
+
+  let import_lines =<< trim END
+    vim9script
+    import That from './Xexport_that.vim'
+    assert_equal('yes', That())
+  END
+  writefile(import_lines, 'Ximport.vim')
+
+  nnoremap <expr> trigger g:Trigger()
+  feedkeys('trigger', "xt")
+
+  delete('Xexport.vim')
+  delete('Ximport.vim')
+  nunmap trigger
+enddef
+
 def Test_vim9script_fails()
   CheckScriptFailure(['scriptversion 2', 'vim9script'], 'E1039:')
   CheckScriptFailure(['vim9script', 'scriptversion 2'], 'E1040:')

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1376,
 /**/
     1375,
 /**/