case-insenstive CONTAINS on .net framework

[donald-hanson]

Is your feature request related to a problem? Please describe.
We are unable to use the case-insensitive CONTAINS call on .net framework because string.Contains(String, StringComparison) was not implemented until .net standard 2.1.

Describe the solution you'd like
Open to any alternative CONTAINS approach compatible with .net framework. One idea includes providing a built-in extension in the CosmosLinqExtensions class like IsDefined or IsPrimitive. Alternatively allow us to write a stub extension method bool Contains(this string input, string value, StringComparison comparison) which the SDK translates.

Describe alternatives you've considered

• Added stub extension method as noted above trying to "trick" the expression visitor.