msglist: Set content font color to match web

With Chrome's web inspector and Mac's "Digital Color Meter", I
verified that our color now matches web's color.

Since GlobalTime's clock icon is a text-like element, change it to
the new color too, and add a content test that makes sure the colors
match each other, and match the DefaultTextStyle that content
elements expect to inherit from.

I didn't find any other text-like elements that need extra treatment
like this.

Author: chrisbobbe

lib/widgets/content.dart

@@ -915,7 +915,10 @@ class GlobalTime extends StatelessWidget {
           child: Row(
             mainAxisSize: MainAxisSize.min,
             children: [
-              Icon(ZulipIcons.clock, size: surroundingFontSize),
+              Icon(
+                size: surroundingFontSize,
+                color: DefaultTextStyle.of(context).style.color!,
+                ZulipIcons.clock),
               // Ad-hoc spacing adjustment per feedback:
               //   https://chat.zulip.org/#narrow/stream/101-design/topic/clock.20icons/near/1729345
               const SizedBox(width: 1),

lib/widgets/message_list.dart

@@ -267,9 +267,7 @@ class _MessageListState extends State<MessageList> with PerAccountStoreAwareStat
     if (!model!.fetched) return const Center(child: CircularProgressIndicator());
 
     return DefaultTextStyle.merge(
-      // TODO figure out text color -- web is supposedly hsl(0deg 0% 20%),
-      //   but seems much darker than that
-      style: const TextStyle(color: Color.fromRGBO(0, 0, 0, 1)),
+      style: TextStyle(color: const HSLColor.fromAHSL(1, 0, 0, 0.15).toColor()),
       // Pad the left and right insets, for small devices in landscape.
       child: SafeArea(
         // Don't let this be the place we pad the bottom inset. When there's

test/widgets/content_test.dart

@@ -614,6 +614,29 @@ void main() {
       tester.widget(find.textContaining(renderedTextRegexp));
     });
 
+    testWidgets('clock icon and text are the same color', (tester) async {
+      await tester.pumpWidget(MaterialApp(home: DefaultTextStyle(
+        style: const TextStyle(color: Colors.green),
+        child: BlockContentList(nodes:
+          parseContent('<p>$timeSpanHtml</p>').nodes),
+      )));
+
+      final icon = tester.widget<Icon>(
+        find.descendant(of: find.byType(GlobalTime),
+          matching: find.byIcon(ZulipIcons.clock)));
+
+      final textSpan = tester.renderObject<RenderParagraph>(
+        find.descendant(of: find.byType(GlobalTime),
+          matching: find.textContaining(renderedTextRegexp)
+      )).text;
+      final textColor = mergedStyleOfSubstring(textSpan, renderedTextRegexp)!.color;
+      check(textColor).isNotNull();
+
+      check(icon).color
+        ..equals(textColor!)
+        ..equals(Colors.green);
+    });
+
     testWidgets('maintains font-size ratio with surrounding text', (tester) async {
       Future<void> doCheck(double Function(GlobalTime widget) sizeFromWidget) async {
         await checkFontSizeRatio(tester,