Set the correct main class on the desugar java_binary target in Bazel.

This will make it easier to build the desugarer tool from the Bazel source tree as an executable (deploy) jar and then use it for something else.

For example, with this CL, you can do the following steps to get a standalone
desugarer binary:

1. git clone https://github.com/bazelbuild/bazel
2. bazel build //src/tools/android/java/com/google/devtools/build/android/desugar:desugar_bin_deploy.jar
3. cp bazel-bin/src/tools/android/java/com/google/devtools/build/android/desugar/desugar_bin_deploy.jar ~/bin/desugar.jar

And then you can invoke desugar without bazel with `java -jar ~/bin/desugar.jar`.

bazelbuild#2975

RELNOTES: None
PiperOrigin-RevId: 155629711

src/tools/android/java/com/google/devtools/build/android/desugar/BUILD

@@ -5,7 +5,7 @@ filegroup(
     name = "embedded_tools",
     srcs = [
         "BUILD.tools",
-        "desugar_bin_deploy.jar",
+        "Desugar_deploy.jar",
     ],
     visibility = ["//src/tools/android/java/com/google/devtools/build/android:__pkg__"],
 )
@@ -28,8 +28,8 @@ java_library(
 )
 
 java_binary(
-    name = "desugar_bin",
-    main_class = "does.not.exist",
+    name = "Desugar",
+    main_class = "com.google.devtools.build.android.desugar.Desugar",
     runtime_deps = [":desugar"],
 )
 

src/tools/android/java/com/google/devtools/build/android/desugar/BUILD.tools

@@ -1,7 +1,9 @@
 package(default_visibility = ["//visibility:public"])
 
+# This target is named "Desugar_embedded" instead of "Desugar" so as to avoid
+# a naming conflict with the existing Desugar_deploy.jar that it depends on.
 java_binary(
-    name = "Desugar",
+    name = "Desugar_embedded",
     main_class = "com.google.devtools.build.android.desugar.Desugar",
-    runtime_deps = [":desugar_bin_deploy.jar"],
-)
+    runtime_deps = [":Desugar_deploy.jar"],
+)

tools/android/BUILD.tools

@@ -42,7 +42,7 @@ alias(
 
 alias(
     name = "desugar_java8",
-    actual = "//src/tools/android/java/com/google/devtools/build/android/desugar:Desugar",
+    actual = "//src/tools/android/java/com/google/devtools/build/android/desugar:Desugar_embedded",
 )
 
 # Bazel puts this on the bootclasspath of android_* targets to support Java 8