dart [nfc]: Specify return types on all methods

This commit covers only where the type is totally boring from the
function's definition: it's the thing that the autofix would insert,
or else it's void and the autofix should insert void.  (But there
seems to be a bug where the autofix doesn't work if the answer should
be void.)

Author: gnprice

lib/widgets/text.dart

@@ -39,7 +39,7 @@ import 'package:flutter/material.dart';
 Typography zulipTypography(BuildContext context) {
   final typography = Theme.of(context).typography;
 
-  convertGeometry(TextTheme inputTextTheme) {
+  TextTheme convertGeometry(TextTheme inputTextTheme) {
     TextTheme result = _weightVariableTextTheme(context, inputTextTheme);
 
     result = _convertTextTheme(result, (maybeInputStyle, _) =>

test/model/autocomplete_test.dart

@@ -66,7 +66,7 @@ void main() {
     ///
     /// For example, "~@chris^" means the text is "@chris", the selection is
     /// collapsed at index 6, and we expect the syntax to start at index 0.
-    doTest(String markedText, MentionAutocompleteQuery? expectedQuery) {
+    void doTest(String markedText, MentionAutocompleteQuery? expectedQuery) {
       final description = expectedQuery != null
         ? 'in ${jsonEncode(markedText)}, query ${jsonEncode(expectedQuery.raw)}'
         : 'no query in ${jsonEncode(markedText)}';
@@ -311,7 +311,7 @@ void main() {
   });
 
   group('MentionAutocompleteQuery.testUser', () {
-    doCheck(String rawQuery, User user, bool expected) {
+    void doCheck(String rawQuery, User user, bool expected) {
       final result = MentionAutocompleteQuery(rawQuery)
         .testUser(user, AutocompleteDataCache());
       expected ? check(result).isTrue() : check(result).isFalse();

test/model/recent_dm_conversations_test.dart

@@ -41,7 +41,7 @@ void main() {
     });
 
     group('message event (new message)', () {
-      setupView() {
+      RecentDmConversationsView setupView() {
         return RecentDmConversationsView(selfUserId: eg.selfUser.userId,
           initial: [
             RecentDmConversation(userIds: [1],    maxMessageId: 200),

test/widgets/compose_box_test.dart

@@ -45,7 +45,7 @@ void main() {
     group('insertPadded', () {
       // Like `parseMarkedText` in test/model/autocomplete_test.dart,
       //   but a bit different -- could maybe deduplicate some.
-      parseMarkedText(String markedText) {
+      TextEditingValue parseMarkedText(String markedText) {
         final textBuffer = StringBuffer();
         int? insertionPoint;
         int i = 0;
@@ -70,7 +70,7 @@ void main() {
       ///
       /// In valueBefore, represent the insertion point as "^".
       /// In expectedValue, represent the collapsed selection as "^".
-      testInsertPadded(String description, String valueBefore, String textToInsert, String expectedValue) {
+      void testInsertPadded(String description, String valueBefore, String textToInsert, String expectedValue) {
         test(description, () {
           final controller = ComposeContentController();
           controller.value = parseMarkedText(valueBefore);

test/widgets/login_test.dart

@@ -27,7 +27,7 @@ void main() {
   group('ServerUrlTextEditingController.tryParse', () {
     final controller = ServerUrlTextEditingController();
 
-    expectUrlFromText(String text, String expectedUrl) {
+    void expectUrlFromText(String text, String expectedUrl) {
       test('text "$text" gives URL "$expectedUrl"', () {
         controller.text = text;
         final result = controller.tryParse();
@@ -36,7 +36,7 @@ void main() {
       });
     }
 
-    expectErrorFromText(String text, ServerUrlValidationError expectedError) {
+    void expectErrorFromText(String text, ServerUrlValidationError expectedError) {
       test('text "$text" gives error "$expectedError"', () {
         controller.text = text;
         final result = controller.tryParse();

test/widgets/text_test.dart

@@ -307,7 +307,7 @@ void main() {
   });
 
   test('wghtFromTextStyle', () {
-    doCheck(TextStyle style, double? expected) {
+    void doCheck(TextStyle style, double? expected) {
       check(wghtFromTextStyle(style)).equals(expected);
     }