Separate annotation processors and include in java as provided

Summary:
With the current setup, the final aar contains `com.facebook.proguard.annotation.DoNotStrip`.  This is not needed (it is only used for proguard), and thus should not get published.

We move proguard annotations into its own project for this, and place it into `java/proguard-annotations`. Here we adopt the gradle convention of `src/main` to make for a nice, clean (one line!) gradle script.  As a different subproject, we can include this to `:yoga` as a `provided` dependency now, which doesn't include it in the output artifact.

Reviewed By: emilsjolander

Differential Revision: D4666572

fbshipit-source-id: a0cb26cb6c264065a0bd355b7d72ba02e3759560

java/com/facebook/proguard/annotations/BUCK

@@ -1,17 +0,0 @@
-# Copyright (c) 2014-present, Facebook, Inc.
-# All rights reserved.
-#
-# This source code is licensed under the BSD-style license found in the
-# LICENSE file in the root directory of this source tree. An additional grant
-# of patent rights can be found in the PATENTS file in the same directory.
-
-include_defs("//YOGA_DEFS")
-
-java_library(
-    name = "annotations",
-    srcs = glob(["*.java"]),
-    source = "1.7",
-    target = "1.7",
-    visibility = [YOGA_ROOT],
-    deps = [],
-)

java/com/facebook/proguard/annotations/DoNotStrip.java

@@ -1,20 +0,0 @@
-/**
- * Copyright (c) 2014-present, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
- */
-
-package com.facebook.proguard.annotations;
-
-import java.lang.annotation.ElementType;
-import java.lang.annotation.Retention;
-import java.lang.annotation.Target;
-
-import static java.lang.annotation.RetentionPolicy.CLASS;
-
-@Target({ ElementType.TYPE, ElementType.FIELD, ElementType.METHOD, ElementType.CONSTRUCTOR })
-@Retention(CLASS)
-public @interface DoNotStrip { }