Make use_key_equivalents opt-in (#21662)

When revamping international keyboard shortcuts I wanted to make the
default to use key equivalents; in hindsight, this is not what people
expect.

Release Notes:

- (Breaking) In keymap.json `"use_layout_keys": true` is now the
default. If you want to opt-out of this behaviour, set
`"use_key_equivalents": true` to have keys mapped for your keyboard. See
[documentation](https://zed.dev/docs/key-bindings#non-qwerty-keyboards)

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Co-authored-by: Peter Tripp <peter@zed.dev>