Notifications: Updating message recreates notification (drops progress bar)

[jrieken]

this continues #50479. as said here there still a few cases missing, esp. 2 looks weird. It seems like the message is interpreted as some kind of default increment, I'd expect an infinite progress in the absence of discrete increments.

        await vscode.window.withProgress(
            {
                location: vscode.ProgressLocation.Notification,
                title: "Test 2: report only message"
            },
            async (progress) => {
                await wait1();
                for (let i = 0; i < 10; ++i) {
                    progress.report({ message: `message ${i}` });
                    await wait2();
                }
            });

[bpasero]

Pushed a change that "fixes" this when the notification is collapsed (which it is by default) because then we notification has a fixed height independent of the content and we can just update the message text directly without splicing the list.

If a notification is expanded the challenge is to adjust the height of the list item (that is used to render notifications) without splicing the item from the list (which is currently not possible). And splicing currently removes the spinning progress from the DOM and adds it back which unfortunately means the animation always starts at 0 again.

[bpasero]

Verification: please look at #50931 (comment) but craft a message that will cause the notification to wrap (i.e. has long text). We still want the notification to grow in height when text overflows.