Deprecation features don't get properly listed on the roadmap page

[mfreed7]

For deprecation features, it's unclear what milestones to use. It seems like the best way to use the tool is:

• When a feature is deprecated (tell people it's going away, but don't break it), that's the start of the "Dev Trial".
• When the feature is removed (can't use it any more), that's the "Shipping" date.

However, when used this way, the roadmap page only shows the deprecation under the milestone where it is going to be removed. Telling people about it at that point is a bit late.

Can we see if the deprecation work flow can be made a bit clearer?

[past]

#2812 is related. We need to prioritize work on deprecations in 2023H2.