Rework MIR drop tree lowering

This PR changes how drops are generated in MIR construction. This is the first half of the fix for rust-lang#47949.

Rather than generating the drops for a given unwind/break/continue/return/generator drop path as soon as they are needed, the required drops are recorded and get generated later.

The motivation for this is
* It simplifies the caching scheme, because it's now possible to walk up the currently scheduled drop tree to recover state.
* The basic block order for MIR more closely resembles execution order.

This PR also:
* Highlights cleanup blocks in the graphviz MIR output.
* Removes some unnecessary drop flag assignments.

…lacrum

Update the `cc` crate

Pulls in updated MSVC detection logic landed in rust-lang/cc-rs#488

…-types-section, r=kinnison,ollie27

Sort "implementations on foreign types" section in the sidebar

Fixes rust-lang#71926.

We were sorting by the ID instead of sorting by the name. They're not in the same order as the implementations but I think it makes more sense this way considering this is what we do for the methods as well.

r? @kinnison

cc @rust-lang/rustdoc

…lan-DPC

Add missing backtick in E0569 explanation

r? @Dylan-DPC