Fetch value(s) from stringified options in tags that stringify options

The `ColorField` `DateTimeField` and `DateField` tags all stringify their option keys before applying their own defaults but they attempt to use the original non-stringified @options to pick values, thus potentially overriding or missing user provided values (if you provide symbols etc)

Replicate-able by `<%= date_field_tag @object, :field, value: Date.today %>` but I couldn't see any tests for this sort of thing so didn't want to bloat the suite.