rust: upgrade to latest rules_rust, cargo-raze (#4872)

Summary:
Upgrading past bazelbuild/rules_rust#643 requires upgrading `cargo-raze`
to pull in google/cargo-raze#400. Happily, the upgrade is easy, so let’s
get this out of the way.

The `cargo-raze` upgrade is needed to set `links = "openssl"` on the
build script for `openssl-sys`. All the other changes are cosmetic, just
modifying comments and reordering `load` statements. To verify:

```
git show -a third_party/ | grep '^[-+]' | grep -v '^\(---\|+++\)' | sort -u
```

wchargin-branch: rules-rust-20210414

.github/workflows/ci.yml

@@ -236,7 +236,7 @@ jobs:
     strategy:
       matrix:
         rust_version: ['1.51.0']
-        cargo_raze_version: ['0.9.2']
+        cargo_raze_version: ['0.12.0']
     steps:
       - uses: actions/checkout@50fbc622fc4ef5163becd7fab6573eac35f8462e
       - name: 'Cache Cargo artifacts'

WORKSPACE

@@ -121,12 +121,12 @@ bazel_version_repository(name = "bazel_version")
 
 http_archive(
     name = "rules_rust",
-    sha256 = "acd759b6fe99a3ae518ea6380e8e95653d27bb9e4a6a2a443abf48cb51fecaa7",
-    strip_prefix = "rules_rust-d468cfa4820a156f850dab957b895d36ee0f4beb",
+    sha256 = "9c7d7fd4378d75232858423d574cff677b16ac9a49cd1a11df545a6e72a315ca",
+    strip_prefix = "rules_rust-42a674093251fb6a603a2652980c9be28a6fea50",
     urls = [
-        # Master branch as of 2021-02-03
-        "http://mirror.tensorflow.org/github.com/bazelbuild/rules_rust/archive/d468cfa4820a156f850dab957b895d36ee0f4beb.tar.gz",
-        "https://github.com/bazelbuild/rules_rust/archive/d468cfa4820a156f850dab957b895d36ee0f4beb.tar.gz",
+        # Master branch as of 2021-04-14
+        "http://mirror.tensorflow.org/github.com/bazelbuild/rules_rust/archive/42a674093251fb6a603a2652980c9be28a6fea50.tar.gz",
+        "https://github.com/bazelbuild/rules_rust/archive/42a674093251fb6a603a2652980c9be28a6fea50.tar.gz",
     ],
 )