Add build progress in Soong UI

Soong UI generates a proto file named build_progress.pb in $(OUT_DIR)
output directory that contains build action numbers (how many are executing,
finished and total) during the course of a build. This is for external
systems that invokes the Platform Build Systems and would like to know
the completion status.

Bug: b/150401146
Test: Wrote a bash script that continuously read the
build_progress.pb file and computed the build completed percentage
while building the aosp_arm-eng target. Compared the percentage between
the Soong output console and the one reported by the bash script.

Change-Id: I7c7347bc8e41958093892d8e2731c4f4169937dd
diff --git a/ui/status/Android.bp b/ui/status/Android.bp
index ec929b3..19e5a2a 100644
--- a/ui/status/Android.bp
+++ b/ui/status/Android.bp
@@ -20,6 +20,7 @@
         "soong-ui-logger",
         "soong-ui-status-ninja_frontend",
         "soong-ui-status-build_error_proto",
+        "soong-ui-status-build_progress_proto",
     ],
     srcs: [
         "critical_path.go",
@@ -53,3 +54,12 @@
         "build_error_proto/build_error.pb.go",
     ],
 }
+
+bootstrap_go_package {
+    name: "soong-ui-status-build_progress_proto",
+    pkgPath: "android/soong/ui/status/build_progress_proto",
+    deps: ["golang-protobuf-proto"],
+    srcs: [
+        "build_progress_proto/build_progress.pb.go",
+    ],
+}