[READY] Rust analyzer code action fixes

[bstaletic]

New rust-analyzer, with the following changes:

1. For the past month and some change, rust-analzer takes advantage of completionItem/resolve requests, but does not advertise that server capability.
   1.1. Link: internal: Send less data during textDocument/completion if possible rust-lang/rust-analyzer#18167 (comment)
2. Sometimes it produces unresolved code action and sometimes it produces a code action literal. Then, if dealing with a code action literal, it errors on codeAction/resolve request.
   2.1. Link: codeAction/resolve throws an exception for a code action without data rust-lang/rust-analyzer#18428
   2.2. This is what the added test exercises.
3. Diagnostics are getting more erratic on startup, so I had to modify the message poll test.

---

This change is 

[bstaletic]

Let's wait on rust-lang/rust-analyzer#18589 so we don't have to introduce new hacks.

[puremourning]

Reviewed 5 of 7 files at r1, 1 of 2 files at r2, 2 of 2 files at r3, all commit messages.
Reviewable status: 1 of 2 LGTMs obtained (waiting on @bstaletic)

---

ycmd/tests/rust/get_completions_proc_macro_test.py line 75 at r2 (raw file):

    for candidate in results:
      if candidate[ 'insertion_text' ] == 'checkpoint':
        checked_candidate = candidate

break?

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.91%. Comparing base (c485180) to head (b96501f).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1771      +/-   ##
==========================================
+ Coverage   95.51%   95.91%   +0.40%     
==========================================
  Files          52       84      +32     
  Lines        6975     8469    +1494     
  Branches        0      163     +163     
==========================================
+ Hits         6662     8123    +1461     
+ Misses        313      296      -17     
- Partials        0       50      +50     

[bstaletic]

Reviewable status: 0 of 2 LGTMs obtained (and 1 stale) (waiting on @puremourning)

---

ycmd/tests/rust/get_completions_proc_macro_test.py line 75 at r2 (raw file):

Previously, puremourning (Ben Jackson) wrote…

break?

Done.

[puremourning]

Reviewed 1 of 1 files at r4, all commit messages.
Reviewable status: 1 of 2 LGTMs obtained (waiting on @bstaletic)

[mergify]

Thanks for sending a PR!