Perform name resolution before and during ast->hir lowering

[jseyfried]

This PR performs name resolution before and during ast->hir lowering instead of in phase 3.
r? @nrc

[nrc]

can you factor out this code dup?

[jseyfried]

Done

[nrc]

A few comments inline (some of which GitHub seems to be hiding due to already being out of date some how). r=me with those addressed.

[KalitaAlexey]

What purpose of it?

[jseyfried]

@KalitaAlexey
Some improvements and a feature require it. Specifically, we want to

• Improve the hir for patterns (hir::PatKind). In particular,
  • Only use the Ident variant for bindings. Currently, it is also used for single identifier unit struct and const patterns, which cannot be distinguished from bindings before resolution.
  • Replace the variant Path with a variant for unit structs/variants a variant for constants.
  • Represent all associated constants with the QPath variant.
• Store PathResolutions (basically, Defs except for associated constants/types) in the hir itself instead of in def_map.
• Implement RFC 1560. We want to be able to use qualified paths in macro invocations and to import macros like items (i.e. with use).

[KalitaAlexey]

@jseyfried Thanks.

[jseyfried]

I could further refactor this into local_def_id (which would return a dummy DefId during testing) and crate_def_with_parent (which would do nothing during testing).

[bors]

☔ The latest upstream changes (presumably #33091) made this pull request unmergeable. Please resolve the merge conflicts.

[jseyfried]

@nrc I finally finished rebasing and fixing fallout in tests and rustdoc. Could you review the last three commits?

[nrc]

@bors: r+

[bors]

📌 Commit 805666a has been approved by nrc

[bors]

⌛ Testing commit 805666a with merge a4d2424...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-32cross-opt, auto-linux-64-cargotest, auto-linux-64-cross-armhf, auto-linux-64-cross-armsf, auto-linux-64-cross-freebsd, auto-linux-64-cross-netbsd, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-opt-mir, auto-linux-64-opt-rustbuild, 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-mac-64-opt-rustbuild, auto-mac-cross-ios-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-32-opt-rustbuild, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-cross-opt, auto-win-msvc-32-opt, auto-win-msvc-64-cargotest, auto-win-msvc-64-opt, auto-win-msvc-64-opt-mir, auto-win-msvc-64-opt-rustbuild