overhaul intra-doc-link ambiguity warning

[euclio]

Fixes #52784.

• Makes the warning part of the intra_doc_link_resolution_failure
  lint.
• Tightens the span to just the ambiguous link.
• Reports ambiguities across all three namespaces.
• Uses structured suggestions for disambiguation.
• Adds a test for the warnings.

r? @QuietMisdreavus

[rust-highfive]

The job mingw-check of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

travis_time:end:02e239a8:start=1551393402098862844,finish=1551393403024057781,duration=925194937
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
Setting environment variables from .travis.yml
$ export IMAGE=mingw-check
---
$ pip install --user awscli; export PATH=$PATH:$HOME/.local/bin:$HOME/Library/Python/2.7/bin/
/usr/local/lib/python2.7/dist-packages/pip/_vendor/requests/__init__.py:83: RequestsDependencyWarning: Old version of cryptography ([1, 2, 3]) may cause slowdown.
  warnings.warn(warning, RequestsDependencyWarning)
Collecting awscli
  Downloading https://files.pythonhosted.org/packages/aa/ea/cb62728e9b38f9d8c620d60815f8dd54ca015f6b9af8f5a3d03d9b2e3c64/awscli-1.16.115-py2.py3-none-any.whl (1.4MB)
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---
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Requirement already satisfied: PyYAML<=3.13,>=3.10 in /usr/lib/python2.7/dist-packages (from awscli) (3.11)
Collecting botocore==1.12.105 (from awscli)
  Downloading https://files.pythonhosted.org/packages/cf/ce/acc9013dee20fc94c9b9ae121f5b7b342a206f0d577be1e5c6129811194a/botocore-1.12.105-py2.py3-none-any.whl (5.3MB)
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---
[00:06:51]    --> src/librustdoc/passes/collect_intra_doc_links.rs:563:21
[00:06:51]     |
[00:06:51] 561 |                     Def::Method(..) | Def::Fn(..) => {
[00:06:51]     |                                                      - close delimiter possibly meant for this
[00:06:51] 562 |                         ("add parentheses", format!("{}()", path_str)
[00:06:51]     |                         - un-closed delimiter
[00:06:51]     |                     ^ incorrect close delimiter
[00:06:51] 
[00:06:55] error: aborting due to previous error
[00:06:55] 
---
travis_time:end:01170a56:start=1551393830096704322,finish=1551393830101886727,duration=5182405
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:332b24d7
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:15227283
travis_time:start:15227283
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:09d8a1e0
$ dmesg | grep -i kill

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[bors]

☔ The latest upstream changes (presumably #58915) made this pull request unmergeable. Please resolve the merge conflicts.

[euclio]

@petrochenkov Comments addressed, ready for another review.

[petrochenkov]

@bors r+

[bors]

📌 Commit 4ac4a966defb942e0792b1704c86ca82fd8bc2e7 has been approved by petrochenkov

[bors]

☔ The latest upstream changes (presumably #56732) made this pull request unmergeable. Please resolve the merge conflicts.

[euclio]

@petrochenkov Rebased.

[petrochenkov]

@bors r+

[bors]

📌 Commit 3bb2275 has been approved by petrochenkov

[Mark-Simulacrum]

This PR (likely in combination with some other PR) failed on CI in the rollup (#59183). Not de-approving because which PR caused the failure I'm not sure.

[euclio]

Looks like #59044 broke this. I can rebase later today.

[euclio]

Rebased, not sure if this needs to be reapproved.

[petrochenkov]

@bors r+

[bors]

📌 Commit 7c66ae2 has been approved by petrochenkov

[petrochenkov]

@euclio
r+ approves a specific commit, so a re-approval is needed when new commits added, or the old ones are changed (e.g. during rebase).

[bors]

⌛ Testing commit 7c66ae2 with merge 03dafa7...

[bors]

☀️ Test successful - checks-travis, status-appveyor
Approved by: petrochenkov
Pushing 03dafa7 to master...