Default annotations_enabled to true for sdk_library

This turns out retention of Nullable annotations, which is almost
certainly what every user wants. Also add the "stub-annotations" lib to
the stub libs property, to make sure the nullability annotations
resolve properly.

Bug: 157010342
Test: m
Change-Id: I905144add4ef6f85445eedd1ba5169445f6005e0

java/sdk_library.go

@@ -789,6 +789,9 @@ func (module *SdkLibrary) createStubsLibrary(mctx android.DefaultableHookContext
 	props.Patch_module = module.properties.Patch_module
 	props.Installable = proptools.BoolPtr(false)
 	props.Libs = module.sdkLibraryProperties.Stub_only_libs
+	// The stub-annotations library contains special versions of the annotations
+	// with CLASS retention policy, so that they're kept around for kotlin.
+	props.Libs = append(props.Libs, "stub-annotations")
 	props.Product_variables.Pdk.Enabled = proptools.BoolPtr(false)
 	props.Openjdk9.Srcs = module.properties.Openjdk9.Srcs
 	props.Openjdk9.Javacflags = module.properties.Openjdk9.Javacflags
@@ -822,6 +825,7 @@ func (module *SdkLibrary) createStubsSourcesAndApi(mctx android.DefaultableHookC
 		Arg_files                        []string
 		Args                             *string
 		Java_version                     *string
+		Annotations_enabled              *bool
 		Merge_annotations_dirs           []string
 		Merge_inclusion_annotations_dirs []string
 		Generate_stubs                   *bool
@@ -872,6 +876,7 @@ func (module *SdkLibrary) createStubsSourcesAndApi(mctx android.DefaultableHookC
 	props.Aidl.Local_include_dirs = module.deviceProperties.Aidl.Local_include_dirs
 	props.Java_version = module.properties.Java_version
 
+	props.Annotations_enabled = proptools.BoolPtr(true)
 	props.Merge_annotations_dirs = module.sdkLibraryProperties.Merge_annotations_dirs
 	props.Merge_inclusion_annotations_dirs = module.sdkLibraryProperties.Merge_inclusion_annotations_dirs