Replace annotation_processors with plugins

Follow bazel's modules for annotation processors by introducing
a java_plugin module type that can contain extra metadata about
the annotation processor, the processor class and a flag to
specify if the annotation processor is compatible with the
turbine optimization.  Deprecate the annotation_processors
property, which took a list of java_library_host modules, in
favor of the plugins property, which takes a list of java_plugin
modules.  The annotation_processors property will be removed
once all uses have been replaced with plugins.

Bug: 77284273
Test: plugin_test.go
Test: m caliper
Change-Id: I37c1e80eba71ae2d6a06199fb102194a51994989

java/plugin.go

@@ -0,0 +1,50 @@
+// Copyright 2019 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package java
+
+import "android/soong/android"
+
+func init() {
+	android.RegisterModuleType("java_plugin", PluginFactory)
+}
+
+// A java_plugin module describes a host java library that will be used by javac as an annotation processor.
+func PluginFactory() android.Module {
+	module := &Plugin{}
+
+	module.AddProperties(
+		&module.Module.properties,
+		&module.Module.protoProperties,
+		&module.pluginProperties)
+
+	InitJavaModule(module, android.HostSupported)
+	return module
+}
+
+type Plugin struct {
+	Library
+
+	pluginProperties PluginProperties
+}
+
+type PluginProperties struct {
+	// The optional name of the class that javac will use to run the annotation processor.
+	Processor_class *string
+
+	// If true, assume the annotation processor will generate classes that are referenced from outside the module.
+	// This necessitates disabling the turbine optimization on modules that use this plugin, which will reduce
+	// parallelism and cause more recompilation for modules that depend on modules that use this plugin.
+	Generates_api *bool
+}