Require that a <_ as Try>::Residual implement the Residual trait

[scottmcm]

The Residual trait was even more experimental than Try, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on <T: Try> might need an extra bound even to use a homogeneous try block with the same output type as T::Output. (Another where will of course be needed to return a different impl Try type still.)

cc #154391

[scottmcm]

There's a more nuanced conversation about whether this should go further and also require

Suggested change

	type Residual: Residual<Self::Output>;
	type Residual: Residual<Self::Output, TryType = Self>;

but that has a variety of implications, so I'd rather leave it for another time rather than this PR.

[rustbot]

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[rustbot]

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[petrochenkov]

r? library

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Failed to set assignee to library: invalid assignee

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[petrochenkov]

r? libs

[jhpratt]

cc @rust-lang/libs-api

r=me on implementation, but it's a design decision for you. imo it's more than reasonable to add this bound.