Move coverage tooling to `//rust/coverage` (#4257)

This mirrors `rules_cc` in an effort to promote consistency among rules
https://github.com/bazelbuild/rules_cc/pull/867

extensions/prost/private/prost.bzl

diff --git a/extensions/prost/private/prost.bzl b/extensions/prost/private/prost.bzl
index bff3092..dec7e55 100644
--- a/extensions/prost/private/prost.bzl
+++ b/extensions/prost/private/prost.bzl
@@ -368,7 +368,7 @@
     attr_aspects = ["deps"],
     attrs = {
         "_collect_cc_coverage": attr.label(
-            default = Label("@rules_rust//util:collect_coverage"),
+            default = Label("@rules_rust//rust/coverage:collect_rust_coverage"),
             executable = True,
             cfg = "exec",
         ),
@@ -432,7 +432,7 @@
             mandatory = True,
         ),
         "_collect_cc_coverage": attr.label(
-            default = Label("@rules_rust//util:collect_coverage"),
+            default = Label("@rules_rust//rust/coverage:collect_rust_coverage"),
             executable = True,
             cfg = "exec",
         ),

rust/coverage/BUILD.bazel

diff --git a/rust/coverage/BUILD.bazel b/rust/coverage/BUILD.bazel
new file mode 100644
index 0000000..a4f37cd
--- /dev/null
+++ b/rust/coverage/BUILD.bazel
@@ -0,0 +1,17 @@
+load("//rust:defs.bzl", "rust_binary")
+
+rust_binary(
+    name = "collect_rust_coverage",
+    srcs = ["collect_rust_coverage.rs"],
+    edition = "2018",
+    # To ensure this tool is produced deterministically, debug info
+    # is stripped out. On macOS, full symbol stripping is needed to
+    # also remove N_OSO stab entries whose timestamps and sandbox
+    # paths vary between builds.
+    rustc_flags = select({
+        "@platforms//os:linux": ["-Cstrip=debuginfo"],
+        "@platforms//os:macos": ["-Cstrip=symbols"],
+        "//conditions:default": [],
+    }),
+    visibility = ["//visibility:public"],
+)

rust/coverage/collect_rust_coverage.rs

diff --git a/util/collect_coverage/collect_coverage.rs b/rust/coverage/collect_rust_coverage.rs
similarity index 100%
rename from util/collect_coverage/collect_coverage.rs
rename to rust/coverage/collect_rust_coverage.rs

rust/private/rust.bzl

diff --git a/rust/private/rust.bzl b/rust/private/rust.bzl
index a69202a..54178d7 100644
--- a/rust/private/rust.bzl
+++ b/rust/private/rust.bzl
@@ -932,7 +932,7 @@
 
 _COVERAGE_ATTRS = {
     "_collect_cc_coverage": attr.label(
-        default = Label("//util/collect_coverage"),
+        default = Label("//rust/coverage:collect_rust_coverage"),
         executable = True,
         cfg = "exec",
     ),
@@ -1308,7 +1308,7 @@
         default = False,
         doc = dedent("""\
             Flag to dynamically link the standard library as a Rust dylib .so object when building this binary.
-            
+
             Default is false. This is often required when building a binary that depends on a Rust ABI dylib.
         """),
     ),

util/collect_coverage/BUILD.bazel

diff --git a/util/collect_coverage/BUILD.bazel b/util/collect_coverage/BUILD.bazel
index 24ed5be..00aab4a 100644
--- a/util/collect_coverage/BUILD.bazel
+++ b/util/collect_coverage/BUILD.bazel
@@ -1,17 +1,6 @@
-load("//rust:defs.bzl", "rust_binary")
-
-rust_binary(
+alias(
     name = "collect_coverage",
-    srcs = ["collect_coverage.rs"],
-    edition = "2018",
-    # To ensure this tool is produced deterministically, debug info
-    # is stripped out. On macOS, full symbol stripping is needed to
-    # also remove N_OSO stab entries whose timestamps and sandbox
-    # paths vary between builds.
-    rustc_flags = select({
-        "@platforms//os:linux": ["-Cstrip=debuginfo"],
-        "@platforms//os:macos": ["-Cstrip=symbols"],
-        "//conditions:default": [],
-    }),
+    actual = "//rust/coverage:collect_rust_coverage",
+    deprecation = "instead use `@rules_rust//rust/coverage:collect_rust_coverage`",
     visibility = ["//visibility:public"],
 )