Fix "Mis-calculated spans" errors from -Z save-analysis + refactoring

[kennytm]

Removed the path span extraction methods from SpanUtils:

• spans_with_brackets
• spans_for_path_segments
• spans_for_ty_params

Use the span fields in PathSegment and TyParam instead.

(Note that since it processes ast::Path not a qualified path (hir::QPath / ast::QSelf), UFCS path will be flattened: <Foo as a::b::c::Trait>::D::E::F::g will be seen as a::b::c::Trait::D::E::F::g.)

Fix #43796. Close #41478.

r? @nrc

[petrochenkov]

Thanks!
@bors r+

[bors]

📌 Commit 03e107f has been approved by petrochenkov

[bors]

⌛ Testing commit 03e107fb2a61f50c4469db6e2ea37c2c2668703f with merge bd64db92d92019a4c15cce7416e385e49b411dc2...

[kennytm]

@petrochenkov Sorry the PR-CI had shown failure, due to the new test case trying to write to a read-only file system. I've force-pushed a new commit. Maybe let's ensure the CI shows a green tick before re-r+'ing 🙂.

[00:51:12] /bin/sh: 1: cannot create stderr.txt: Read-only file system
[00:51:12] cat: stderr.txt: No such file or directory

---

@bors retry (stop the test, go to the next PR.)

[petrochenkov]

All checks have passed

@bors r+

[bors]

📌 Commit a017b07 has been approved by petrochenkov

[bors]

⌛ Testing commit a017b079e94654af35570d6ddcb5b25bbc797229 with merge 924b9811d1b81b8eefec894e3818e0932673dcaf...

[bors]

💔 Test failed - status-appveyor

[kennytm]

@petrochenkov The Windows error should be fixed now, hopefully. run-make test is hard :(

[petrochenkov]

@bors r+

[bors]

📌 Commit 60377e4 has been approved by petrochenkov

[bors]

⌛ Testing commit 60377e4 with merge df511d5...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: petrochenkov
Pushing df511d5 to master...