breaking: bump project requirements

[erisu]

Motivation and Context

Bump the project requirements.

• Cordova Android >= 9.0.0
• Cordova CLI >= 9.0.0

Note: Changes also include #627. This PR should be rebased after #627 is merged in.

[erisu]

@jcesarmobile Any thoughts on iOS requirements being set to 6.x?

I don't know if there are any breaking changes on the iOS side of this plugin, but from the current testing system standpoint (paramedic) I believe it always checks out the latest Cordova iOS (6.x) which requires Xcode 11 to be used. This means we might be only testing Xcode 11+... At least the additional tests do not pass on any version below Xcode 11.

[jcesarmobile]

I think we should require cordova-ios 5.1.0, I see no reason to require 6.0.0 in this plugin.

Not being able to test on Xcode 10 is not a big problem, considering Apple requires Xcode 11 to submit apps.

I've created a thread on the mail list to talk about the engines and used this PR as an example of what I think we should be doing.

[erisu]

@jcesarmobile I set it to cordova-ios >= 5.1.0 as you mentioned in previous comment but also debated if it should really be >= 5.1.1. 5.1.0 had a bug with the new WKWebViewOnly flag being set and prepare running before the platform actually existing. Or something like this if memory is correct. But 5.1.1 fix that prepare issue surrounding the flag.

Other than that, this PR I think is OK.

[jcesarmobile]

I guess if people face the prepare bug will update from 5.1.0 to 5.1.1, but you can set it to 5.1.1 if you prefer