remote: introduce --disk_cache_flag

Consolidate the --experimental_local_disk_cache and --experimental_local_disk_cache_path
flags into a single --disk_cache= flag. Also, create the cache directory
if it doesn't exist.

RELNOTES: We replaced the --experimental_local_disk_cache and
--experimental_local_disk_cache_path flags into a single --disk_cache
flag. Additionally, Bazel now tries to create the disk cache directory
if it doesn't exist.

Closes #5119.

PiperOrigin-RevId: 195070550
diff --git a/src/main/java/com/google/devtools/build/lib/remote/RemoteOptions.java b/src/main/java/com/google/devtools/build/lib/remote/RemoteOptions.java
index dd4f5a0..e3b303d 100644
--- a/src/main/java/com/google/devtools/build/lib/remote/RemoteOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/remote/RemoteOptions.java
@@ -175,25 +175,17 @@
   )
   public boolean experimentalRemoteSpawnCache;
 
-  // TODO(davido): Find a better place for this and the next option.
   @Option(
-    name = "experimental_local_disk_cache",
-    defaultValue = "false",
-    documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
-    effectTags = {OptionEffectTag.UNKNOWN},
-    help = "Whether to use the experimental local disk cache."
-  )
-  public boolean experimentalLocalDiskCache;
-
-  @Option(
-    name = "experimental_local_disk_cache_path",
+    name = "disk_cache",
     defaultValue = "null",
     documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
     effectTags = {OptionEffectTag.UNKNOWN},
     converter = OptionsUtils.PathFragmentConverter.class,
-    help = "A file path to a local disk cache."
+    help =
+        "A path to a directory where Bazel can read and write actions and action outputs. "
+            + "If the directory does not exist, it will be created."
   )
-  public PathFragment experimentalLocalDiskCachePath;
+  public PathFragment diskCache;
 
   @Option(
     name = "experimental_guard_against_concurrent_changes",