set KeyboardInput::repeat to true for forwarded repeat events

[cxreiff]

Bevy merged a PR adding a repeat boolean to the KeyboardInput struct, corresponding to an equivalent concept in winit. When forwarding crossterm events we should correctly set this flag when reported by the terminal or we can reasonably identify a repeat event as part of our emulation strategy.

Holding off on a PR until events are refactored, just opening this to keep this bevy input change on the radar as I'm not sure if it will be mentioned in 0.15 migration materials.

(Side conversation: how should changes like this and the event refactor, that depend on unreleased changes in bevy, be handled with release-plz? Should a separate 0.15 branch be kept?)