Auto merge of #100966 - compiler-errors:revert-remove-deferred-sized-checks, r=pnkfelix

Revert "Remove deferred sized checks"

cc: rust-lang/rust#100652 (comment)

I'm okay with reverting this for now, and I will look into the diagnostic regressions.

This reverts commit 33212bf.

r? `@pnkfelix`

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EDIT: This _also_ fixes #101066, a regression in method selection logic/coercion(?) due to the early registering of a `Sized` bound.

Author: bors