InitialValue and pass key to super

[percula]

I've been using this excellent package for awhile, with changes 1 and 2 in production for years with no issues. I figured it's time to commit these changes back to this repo if you'll have them:

1. The initialValue wasn't being set correctly, so I've added a few lines to set it in the state.
2. Change default lastDate to be simply 5 days later, rather than 5 years later.
3. Pass along key to super. I needed this to programmatically clear the date.

[Cali0707]

Hi @percula thanks for opening the PR, and I'm sorry I did not get around to reviewing this sooner. Would you be able to provide an example of when the initialValue wasn't being set properly? I haven't been able to recreate this issue myself locally.

[percula]

Hi @Cali0707 , sorry for my tardiness too! I've created a sample project showing the issue. When the initialvalue is set at widget creation, there isn't an issue. However, if initialvalue is set after widget creation, perhaps by Provider or an async method, it won't display in the TextField. The range will show up just fine in the dialog though.

In the sample project, I've modified the FAB to set the initialValue, to easily replicate the issue: