Output Javadoc comments for public API

When generating stubs source for contributions to the public API keep
the Javadoc comments from the input source so that the stubs source can
be used as input to the metalava invocation that creates the stubs from
which the public Javadoc is generated.

This is needed to fix an issue with conscrypt's contributions to the
public API, i.e. SSLEngines and SSLSockets where the Javadoc comments
were not present in the generated Javadoc.

Test: Built offline-sdk-docs with and without the change and
      diffed them. The only difference was the timestamp.js
      file and they now included proper documentation for the
      SSLEngines/SSLSockets classes.
Bug: 169162018
Change-Id: I1b50cff3b91766ce261b2f8e798b77ebc6faac70

java/droiddoc.go

@@ -253,6 +253,10 @@ type DroidstubsProperties struct {
 	// if set to true, allow Metalava to generate doc_stubs source files. Defaults to false.
 	Create_doc_stubs *bool
 
+	// if set to true, cause Metalava to output Javadoc comments in the stubs source files. Defaults to false.
+	// Has no effect if create_doc_stubs: true.
+	Output_javadoc_comments *bool
+
 	// if set to false then do not write out stubs. Defaults to true.
 	//
 	// TODO(b/146727827): Remove capability when we do not need to generate stubs and API separately.
@@ -1150,7 +1154,9 @@ func (d *Droidstubs) stubsFlags(ctx android.ModuleContext, cmd *android.RuleBuil
 			cmd.FlagWithArg("--doc-stubs ", stubsDir.String())
 		} else {
 			cmd.FlagWithArg("--stubs ", stubsDir.String())
-			cmd.Flag("--exclude-documentation-from-stubs")
+			if !Bool(d.properties.Output_javadoc_comments) {
+				cmd.Flag("--exclude-documentation-from-stubs")
+			}
 		}
 	}
 }

java/sdk_library.go

@@ -1203,6 +1203,7 @@ func (module *SdkLibrary) createStubsSourcesAndApi(mctx android.DefaultableHookC
 		Sdk_version                      *string
 		System_modules                   *string
 		Libs                             []string
+		Output_javadoc_comments          *bool
 		Arg_files                        []string
 		Args                             *string
 		Java_version                     *string
@@ -1278,6 +1279,11 @@ func (module *SdkLibrary) createStubsSourcesAndApi(mctx android.DefaultableHookC
 	}
 	droidstubsArgs = append(droidstubsArgs, android.JoinWithPrefix(disabledWarnings, "--hide "))
 
+	// Output Javadoc comments for public scope.
+	if apiScope == apiScopePublic {
+		props.Output_javadoc_comments = proptools.BoolPtr(true)
+	}
+
 	// Add in scope specific arguments.
 	droidstubsArgs = append(droidstubsArgs, scopeSpecificDroidstubsArgs...)
 	props.Arg_files = module.sdkLibraryProperties.Droiddoc_option_files