patch 8.2.4257: Vim9: finding global function without g: prefix inconsistent

Problem:    Vim9: finding global function without g: prefix but not finding
            global variable is inconsistent.
Solution:   Require using g: for a global function.  Change the vim9.vim
            script into a Vim9 script with exports.  Fix that import in legacy
            script does not work.
diff --git a/src/testdir/test_normal.vim b/src/testdir/test_normal.vim
index 9fcc9fd..2ed6a80 100644
--- a/src/testdir/test_normal.vim
+++ b/src/testdir/test_normal.vim
@@ -3,7 +3,7 @@
 source shared.vim
 source check.vim
 source view_util.vim
-source vim9.vim
+import './vim9.vim' as v9
 
 func Setup_NewWindow()
   10new
@@ -626,7 +626,7 @@
     normal! g@l
     call assert_equal([23, 'char'], g:OpFunc1Args)
   END
-  call CheckTransLegacySuccess(lines)
+  call v9.CheckTransLegacySuccess(lines)
 
   " Test for using a script-local function name
   func s:OpFunc3(type)
@@ -693,7 +693,7 @@
     assert_equal(['char'], g:LocalOpFuncArgs)
     bw!
   END
-  call CheckScriptSuccess(lines)
+  call v9.CheckScriptSuccess(lines)
 
   " setting 'opfunc' to a script local function outside of a script context
   " should fail