This fixes two issues in the REPL when it is started with a new context
(useGlobal option set to false):

• The primordials object does not contain all builtins, so the
  filtering based on property names from primordials was wrong.
• The autocompleter did not take builtin names into account because
  they are not properties of the context object.

A list of all global builtin names is created lazily when needed. It is
used for filtering for the copy and for adding those names to the
autocompleter list.

Fixes: #30792

I did not add a new test because this will be covered when #30740 has landed.