Duplicated modules and functions in solana_sdk docs

[brson]

Problem

The crate documentation for solana_sdk lists duplicate modules for entrypoint, feature, and many other items. This arises because solana_sdk is glob-reexporting solana_program::* but also redefining several of the items within that crate. Rust callers only see the redefinitions but due to a bug (rust-lang/rust#60522) in rustdoc, the documentation shows two definitions.

Clicking either definition leads to the same page. The linked issue indicates that whether rustdoc shows the reexport or the redefinition is non-deterministic, but so far I have only seen rustdoc show the redefinitions in this case.

Proposed Solution

While fixing the bug upstream would be best, I intend to just add #[doc(hidden)] to the redefinitions to work around the problem.

[brson]

Some of the redefinitions can probably be eliminated by moving their defs into solana_program.

[brson]

After looking into this a bit more I think using #[doc(hidden)] here will just make a bigger mess. I am seeing that sometimes rustdoc generates the correct docs, for the duplicated solana_sdk modules, and sometimes the incorrect docs, for the imported solana_program modules. It's pretty confusing. It would be best to try to fix this upstream, and if not, to change the * imports to enumerate every import explicitly.