Add C-x C-f behaviour for Vim users

[tuhdo]

In Vim, when you press C-x C-f, it auto-completes paths. We can have the same feature by using company-files. Unfortunately, company is not allowed to enable globally. Maybe we can make it works:

1. Create a command that stores previous company-mode variable, then add a hook to company-completion-finished-hook to restore the mode back to how it was.
2. Enable company globally, but for non-officially supported buffers, we only allow rudimentary backends that are related to text. If we do this, it would be much easier.

[syl20bnr]

I would go for 1, should be easy enough with a macro with-temp-mode that we could store in core-funcs.el.

[github-actions]

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