Add exported_plugins to java.Library.

The behaviour is similar to go/be#java_library.exported_plugins. Plugins added to exported_plugins of library X are not applied to the library itself, but rather to libraries that directly depend on the library X.

Test: m checkbuild
Bug: 139740873
Change-Id: I4042bd482ad9cb12d6fbaac51f039d38b1b7a428

java/device_host_converter.go

@@ -162,6 +162,10 @@ func (d *DeviceHostConverter) ExportedSdkLibs() []string {
 	return nil
 }
 
+func (d *DeviceHostConverter) ExportedPlugins() (android.Paths, []string) {
+	return nil, nil
+}
+
 func (d *DeviceHostConverter) SrcJarArgs() ([]string, android.Paths) {
 	return d.srcJarArgs, d.srcJarDeps
 }