move const block checks before lowering step

[oli-obk]

this makes sure the checks run before typeck (which might use the constant or const
function to calculate an array length) and gives prettier error messages in case of for
loops and such (since they aren't expanded yet).

fixes #30887

r? @pnkfelix

[rust-highfive]

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[arielb1]

I had the idea for a librustc_checks crate called librustc_passes

[arielb1]

I think that is a better name.

[oli-obk]

I'm totally emotionless about the name. I just got annoyed with the long build times rebuilding librustc when it doesn`t depend on the check.

[arielb1]

That was what I guessed. I wanted to move the solely-changing passes there so that they can be compiled in parallel with librustc_xyz.

[oli-obk]

renamed crate to librustc_passes

[arielb1]

@bors r+

[bors]

📌 Commit 1471d93 has been approved by arielb1

[bors]

⌛ Testing commit 1471d93 with merge 83c3b7f...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt