patch 8.2.4510: Vim9: shortening commands leads to confusing script

Problem:    Vim9: shortening commands leads to confusing script.
Solution:   In Vim9 script require at least ":cont" for ":continue", "const"
            instead of "cons", "break" instead of "brea", "catch" instead of
            "cat", "else" instead of "el" "elseif" instead of "elsei" "endfor"
            instead of "endfo" "endif" instead of "en" "endtry" instead of
            "endt", "finally" instead of "fina", "throw" instead of "th",
            "while" instead of "wh".

src/testdir/test_vim9_script.vim

@@ -460,7 +460,7 @@ def Test_try_catch_throw()
     endtry
   catch /wrong/
     add(l, 'caught')
-  fina
+  finally
     add(l, 'finally')
   endtry
   assert_equal(['1', 'caught', 'finally'], l)
@@ -1004,7 +1004,7 @@ enddef
 def s:ReturnFinally(): string
   try
     return 'intry'
-  finall
+  finally
     g:in_finally = 'finally'
   endtry
   return 'end'
@@ -3374,6 +3374,37 @@ def Run_test_reject_declaration()
   g:StopVimInTerminal(buf)
 enddef
 
+def Test_minimal_command_name_length()
+  var names = [
+       'cons',
+       'brea',
+       'cat',
+       'catc',
+       'con',
+       'el',
+       'els',
+       'elsei',
+       'endfo',
+       'en',
+       'end',
+       'endi',
+       'endw',
+       'endt',
+       'endtr',
+       'fina',
+       'finall',
+       'th',
+       'thr',
+       'thro',
+       'wh',
+       'whi',
+       'whil',
+      ]
+  for name in names
+    v9.CheckDefAndScriptFailure([name .. ' '], 'E1065:')
+  endfor
+enddef
+
 def Test_unset_any_variable()
   var lines =<< trim END
     var name: any