Problem:
`diagnostic.status` only follows the `config.status.format` setting to determine how to display diagnostic signs. However, `signs` can actually also be configured via `config.signs.text`.
Solution:
If the user has set symbols via `config.status.format`, let that determine the content of `signs`; otherwise, use `config.signs.text` for display.
TODO: drop support `type(config.status.format) == 'table'`; users should just configure `config.signs.text` directly.
b56f7c6edd
