patch 8.2.3178: Vim9: the file name of an :import cannot be an expression

Problem:    Vim9: the file name of an :import cannot be an expression.
Solution:   Accept an expression that results in a string.  Do not support
            :import in a function.

src/testdir/test_vim9_script.vim

@@ -1085,7 +1085,9 @@ def Test_vim9_import_export()
     enddef
     g:funcref_result = GetExported()
 
-    import {exp_name} from './Xexport.vim'
+    var dir = './'
+    var ext = ".vim"
+    import {exp_name} from dir .. 'Xexport' .. ext
     g:imported_name = exp_name
     exp_name ..= ' Doe'
     g:imported_name_appended = exp_name
@@ -1148,26 +1150,6 @@ def Test_vim9_import_export()
   unlet g:imported_func
   delete('Ximport_lbr.vim')
 
-  # import inside :def function
-  var import_in_def_lines =<< trim END
-    vim9script
-    def ImportInDef()
-      import exported from './Xexport.vim'
-      g:imported = exported
-      exported += 7
-      g:imported_added = exported
-    enddef
-    ImportInDef()
-  END
-  writefile(import_in_def_lines, 'Ximport2.vim')
-  source Ximport2.vim
-  # TODO: this should be 9879
-  assert_equal(9876, g:imported)
-  assert_equal(9883, g:imported_added)
-  unlet g:imported
-  unlet g:imported_added
-  delete('Ximport2.vim')
-
   var import_star_as_lines =<< trim END
     vim9script
     import * as Export from './Xexport.vim'
@@ -1181,8 +1163,9 @@ def Test_vim9_import_export()
   END
   writefile(import_star_as_lines, 'Ximport.vim')
   source Ximport.vim
-  assert_equal(9883, g:imported_def)
-  assert_equal(9883, g:imported_script)
+  # FIXME: this should be 9881
+  assert_equal(9876, g:imported_def)
+  assert_equal(9876, g:imported_script)
 
   var import_star_as_lines_no_dot =<< trim END
     vim9script
@@ -1257,7 +1240,7 @@ def Test_vim9_import_export()
   END
   writefile(import_star_as_lbr_lines, 'Ximport.vim')
   source Ximport.vim
-  assert_equal(9883, g:imported)
+  assert_equal(9876, g:imported)
 
   var import_star_lines =<< trim END
     vim9script
@@ -1345,7 +1328,7 @@ def Test_vim9_import_export()
     import name from Xexport.vim
   END
   writefile(import_invalid_string_lines, 'Ximport.vim')
-  assert_fails('source Ximport.vim', 'E1071:', '', 2, 'Ximport.vim')
+  assert_fails('source Ximport.vim', 'E121:', '', 2, 'Ximport.vim')
 
   var import_wrong_name_lines =<< trim END
     vim9script
@@ -1659,22 +1642,6 @@ def Test_vim9script_reload_import()
   source Xreload.vim
   source Xreload.vim
 
-  var testlines =<< trim END
-    vim9script
-    def TheFunc()
-      import GetValtwo from './Xreload.vim'
-      assert_equal(222, GetValtwo())
-    enddef
-    TheFunc()
-  END
-  writefile(testlines, 'Ximport.vim')
-  source Ximport.vim
-
-  # Test that when not using "morelines" GetValtwo() and valtwo are still
-  # defined, because import doesn't reload a script.
-  writefile(lines, 'Xreload.vim')
-  source Ximport.vim
-
   # cannot declare a var twice
   lines =<< trim END
     vim9script