[Feature Request] Make Shared Model SDKs more lenient in card parsing

What is the problem you are attempting to solve with this feature?

There is a implementation difference between Adaptive Cards SDKs where shared model SDKs are more strict, in terms of Card parsing, than the JS version. This leads to many issues in Teams where Cards will render correctly in desktop but fail in the mobile apps, which causes a large support cost (actualized and developer-time) for Teams.

A description of your proposed solution to the problem

The AC SDKs need to normalize on a single standard of strict-ness of Card parsing. Due to the large existing customer base and existing scenarios, the only viable path is to match the Javascript strict-ness in the mobile SDKs; this is the only path forward because the other approach would break existing users without any change to their Cards, which would not be a good user experience.

No files, tests, or entry points are named. Start by comparing card parsing behavior in the shared model SDKs with the JavaScript SDK, focusing on the strictness difference that affects Teams mobile apps. Done means the mobile SDKs accept the same cards as the JavaScript version without breaking existing scenarios.