FlexObject indexer returns dynamic which forces dynamic programming model even if developer wants to stick to strongly typed model

[drub0y]

Currently the indexer of the FlexObject class is typed as dynamic. The problem with this is that, as a .NET developer, if I'm choosing not to use the dynamic programming model of FlexObject and am trying to get/set values through the indexer, it is "forcing" me into the dynamic model.

The indexer should instead be typed as object which would prevent developers being opted into the dynamic model when they don't want/need to be. Note that this doesn't prevent them from treating the values coming out of the indexer as dynamic if they want to, it just won't force it any more.

[cleemullins]

FlexObject has been fully removed in #425