Follow up to cached run_system

[SkiFire13]

Objective

• Fixes run_system_cached API will reject systems created by pipe and map #15373
• Fixes Add cached run_system API #14920 (comment)

Solution

• Make IntoSystem::pipe and IntoSystem::map return two new (possibly-ZST) types that implement IntoSystem and whose into_system method return the systems that were previously being returned by IntoSystem::pipe and IntoSystem::map
• Don't eagerly call IntoSystem::into_system on the argument given to RunSystemCachedWith::new to avoid losing its ZST-ness

Testing

• Added a regression test for each issue

Migration Guide

• IntoSystem::pipe and IntoSystem::map now return IntoPipeSystem and IntoAdapterSystem instead of PipeSystem and AdapterSystem. Most notably these types don't implement System but rather only IntoSystem.

[alice-i-cecile]

Very nice, thank you! I particularly appreciate the regression tests.