Change return signature of router navigate() and navigateToRoute() from boolean to NavigationResult

[matthewcorven]

Fix for #648 to correct typings. Calllers of navigate()/navigateToRoute() could await the routing to complete, but didn't know it due to typings. @davismj

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[matthewcorven]

@davismj and perhaps type NavigationResult would be more clearly named AwaitableNavigationResult?

[davismj]

@matthewcorven thx for the PR, definitely helps me see what's up.

I think the fix needs to be a bit more robust here. It starts in history / browser where navigate has a boolean return type (https://github.com/aurelia/history/blob/master/src/index.js#L56, https://github.com/aurelia/history-browser/blob/master/src/browser-history.ts#L54), which is only accepted because of other insufficient typings around history options (https://github.com/aurelia/history-browser/blob/master/src/browser-history.ts#L111, https://github.com/aurelia/history-browser/blob/master/src/browser-history.ts#L297, https://github.com/aurelia/history-browser/blob/master/src/browser-history.ts#L54).

Additionally, I don't like the NavigationResult typing. Consuming one requires testing for a Promise first: const result: boolean = await Promise.resolve(this.router.navigate('foo');. This implementation detail should not be the burden of an end developer, who should simply be able to await the method.

I'll go ahead and fix this in all three libraries by:

• Adding a typing for NavigationResult in aurelia-history
• Adding a typing for HistoryOptions in aurelia-history-browser
• Enforcing Promise<NavigationResult> return types on all navigation methods in all libraries

This will be a breaking change. Currently, the NavigationResult type includes PipelineResult | boolean, which is a difficult type to work with. I will unify them as NavigationResult = { completed: boolean }, and transform all flat boolean returns into a NavigationResult. This means, moving forward, any navigation results, no matter where they come from, can be consumed like this:

const { completed } = await router.navigate('foo');

[matthewcorven]

Thanks @davismj !