Linux: Rewrite the event loop using calloop (#8314)

This PR unifies the event loop code for Wayland and X11. On Wayland,
blocking dispatch is now used. On X11, the invisible window is no longer
needed.

Release Notes:

- N/A

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Co-authored-by: Dzmitry Malyshau <kvark@fastmail.com>
Co-authored-by: Tadeo Kondrak <me@tadeo.ca>
Co-authored-by: Mikayla Maki <mikayla@zed.dev>
Co-authored-by: julia <julia@zed.dev>