perspective-migrate 5.9.1

Upgrades persisted Perspective `ViewConfig`, `<perspective-viewer>` and workspace configs from any release since 2.0 to the current schema.
Documentation
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// ┃ ██████ ██████ ██████       █      █      █      █      █ █▄  ▀███ █       ┃
// ┃ ▄▄▄▄▄█ █▄▄▄▄▄ ▄▄▄▄▄█  ▀▀▀▀▀█▀▀▀▀▀ █ ▀▀▀▀▀█ ████████▌▐███ ███▄  ▀█ █ ▀▀▀▀▀ ┃
// ┃ █▀▀▀▀▀ █▀▀▀▀▀ █▀██▀▀ ▄▄▄▄▄ █ ▄▄▄▄▄█ ▄▄▄▄▄█ ████████▌▐███ █████▄   █ ▄▄▄▄▄ ┃
// ┃ █      ██████ █  ▀█▄       █ ██████      █      ███▌▐███ ███████▄ █       ┃
// ┣━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┫
// ┃ Copyright (c) 2017, the Perspective Authors.                              ┃
// ┃ ╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌ ┃
// ┃ This file is part of the Perspective library, distributed under the terms ┃
// ┃ of the [Apache License 2.0](https://www.apache.org/licenses/LICENSE-2.0). ┃
// ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛

use serde_json::{Map, Value};

pub(crate) fn escape(segment: &str) -> String {
    segment.replace('~', "~0").replace('/', "~1")
}

pub(crate) fn object_mut<'a>(
    map: &'a mut Map<String, Value>,
    key: &str,
) -> Option<&'a mut Map<String, Value>> {
    map.get_mut(key).and_then(Value::as_object_mut)
}

pub(crate) fn column_styles(
    token: &mut Map<String, Value>,
) -> impl Iterator<Item = (&String, &mut Map<String, Value>)> {
    object_mut(token, "columns_config")
        .into_iter()
        .flat_map(|config| config.iter_mut())
        .filter_map(|(name, style)| style.as_object_mut().map(|style| (name, style)))
}

pub(crate) fn rename(map: &mut Map<String, Value>, from: &str, to: &str) -> Option<Value> {
    let value = map.shift_remove(from)?;
    if map.contains_key(to) {
        Some(value)
    } else {
        map.insert(to.to_owned(), value);
        None
    }
}