List all structs that concretely contain a type

[Havvy]

For structs, unions, and enums include a section Types Containing that lists all of the structs, unions, and enums containing that type concretely.

For traits, do the same but call the section Types Containing Trait Objects.

For example, say we have the following code:

struct Contained;

struct ContainerOf(Contained);

then the Contained documentation would have a section Types Containing that has a list item ContainerOf that links to that structs documentation.

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Note that there is no expectation that this be done anytime soon.