NonStringIndexOption should not default to No

[gmarz]

We default the nullable argument for Index() on our property descriptors to No which doesn't make sense (for instance here and here).

The default in ES is to index, so calling Index() without passing No does the opposite of what you expect.

We should deprecate this in 2.x and remove it the method completely in 5.x. I think something along the lines of NotIndexed() (can't think of a better name at the moment) makes more sense, similar to how we have NotAnalyzed().

[gmarz]

This doesn't apply to 5.0 (see #2025).

[gmarz]

Closed via #2026