Replace remote_cache_hits with more detailed runner_count.

Improvement on #7714.

```
$ bazel build --internal_spawn_scheduler --strategy=Javac=dynamic --config=remote --build_event_json_file=/tmp/bep.json //src:bazel
$ cat /tmp/bep.json | jq '.buildMetrics.actionSummary.runnerCount | select( . != null)'
[
  {
    "name": "total",
    "count": 2698
  },
  {
    "name": "remote cache hit",
    "count": 2259
  },
  {
    "name": "internal",
    "count": 60
  },
  {
    "name": "local",
    "count": 1
  },
  {
    "name": "remote",
    "count": 63
  },
  {
    "name": "worker",
    "count": 315
  }
]
```

PiperOrigin-RevId: 385725354

Author: meisterT

src/main/java/com/google/devtools/build/lib/buildeventstream/proto/build_event_stream.proto

@@ -836,9 +836,6 @@ message BuildMetrics {
     // remote cache hits, but excludes local action cache hits.
     int64 actions_executed = 2;
 
-    // The total number of remote cache hits.
-    int64 remote_cache_hits = 5;
-
     message ActionData {
       string mnemonic = 1;
 
@@ -856,6 +853,15 @@ message BuildMetrics {
     }
     // Contains the top N actions by number of actions executed.
     repeated ActionData action_data = 4;
+
+    // Deprecated. The total number of remote cache hits.
+    int64 remote_cache_hits = 5 [deprecated = true];
+
+    message RunnerCount {
+      string name = 1;
+      int32 count = 2;
+    }
+    repeated RunnerCount runner_count = 6;
   }
   ActionSummary action_summary = 1;
 

src/main/java/com/google/devtools/build/lib/metrics/MetricsCollector.java

@@ -27,6 +27,7 @@
 import com.google.devtools.build.lib.buildeventstream.BuildEventStreamProtos.BuildMetrics;
 import com.google.devtools.build.lib.buildeventstream.BuildEventStreamProtos.BuildMetrics.ActionSummary;
 import com.google.devtools.build.lib.buildeventstream.BuildEventStreamProtos.BuildMetrics.ActionSummary.ActionData;
+import com.google.devtools.build.lib.buildeventstream.BuildEventStreamProtos.BuildMetrics.ActionSummary.RunnerCount;
 import com.google.devtools.build.lib.buildeventstream.BuildEventStreamProtos.BuildMetrics.ArtifactMetrics;
 import com.google.devtools.build.lib.buildeventstream.BuildEventStreamProtos.BuildMetrics.BuildGraphMetrics;
 import com.google.devtools.build.lib.buildeventstream.BuildEventStreamProtos.BuildMetrics.CumulativeMetrics;
@@ -236,10 +237,16 @@ private ActionSummary finishActionSummary() {
                             action.lastEnded.longValue()))
                     .setActionsExecuted(action.numActions.get())
                     .build()));
+
     ImmutableMap<String, Integer> spawnSummary = spawnStats.getSummary();
-    Integer total = spawnSummary.getOrDefault("total", 0);
-    Integer remoteCacheHits = spawnSummary.getOrDefault("remote cache hit", 0);
-    return actionSummary.setActionsExecuted(total).setRemoteCacheHits(remoteCacheHits).build();
+    actionSummary.setActionsExecuted(spawnSummary.getOrDefault("total", 0));
+    spawnSummary
+        .entrySet()
+        .forEach(
+            e ->
+                actionSummary.addRunnerCount(
+                    RunnerCount.newBuilder().setName(e.getKey()).setCount(e.getValue()).build()));
+    return actionSummary.build();
   }
 
   private MemoryMetrics createMemoryMetrics() {