Fix wildcard completion

[rqdmap]

Fix https://github.com/hrsh7th/cmp-cmdline/issues/91

[liskin]

This fixes wildcard completion and also expansion of % and the like, but it breaks many other usecases. Try completing :echo & or :lua vim.treesitter.get_. It'll drop parts of the command line that shouldn't be dropped.

For an in-depth explanation of what a proper fix might look like, see https://github.com/hrsh7th/cmp-cmdline/pull/83#issuecomment-2323332695