When disabling an alert, the background `alertEnabledness` state of the
alert was being set to `undefined` instead of `false`. This didn't have
any user-facing effect, since `undefined` is falsey, but it did result
in a PropType error on the Alert settings page. This mistake was made
in #8550.
The `alertEnabledness` state is now correctly set to `false` instead of
`undefined`.
The unconnected account alert can now be disabled. A "don't show this
again" checkbox has been added to the alert, which prevents that alert
from being shown in the future.
An alert settings page has been added to the settings as well. This
page allows the user to disable or enable any alert.
An alert is now shown when the user switches from an account that is
connected to the active tab to an account that is not connected. The
alert prompts the user to dismiss the alert or connect the account
they're switching to.
The "loading" state is handled by disabling the buttons, and the error
state is handled by displaying a generic error message and disabling
the connect button.
The new reducer for this alert has been created with `createSlice` from
the Redux Toolkit. This utility is recommended by the Redux team, and
represents a new style of writing reducers that I hope we will use more
in the future (or at least something similar). `createSlice` constructs
a reducer, actions, and action creators automatically. The reducer is
constructed using their `createReducer` helper, which uses Immer to
allow directly mutating the state in the reducer but exposing these
changes as immutable.
