Epic: Modernize PM UI & PMC status notifications

[donnie-msft]

The Package Manager UI (PackageManagerControl) and Package Manager Console (ConsoleContainer) today surface status notifications as bespoke WPF *Bar.xaml UserControls.
These predate the VS Fluent InfoBar and the Task Status Center (TSC), so they have an inconsistent look & feel, carry custom rendering/animation/keyboard code.

The goal is to stop conflating two very different kinds of information: static notification messages and live status/progress indications.

This epic tracks reducing and modernizing these notifications under one guiding principle:

If it's static text, convert it to a Fluent VS InfoBar. If it's dynamic content (progress / live status), move it to the Task Status Center (TSC).

Notifications to migrate

Bar	Host(s)	What changes
RestartRequestBar	PM UI + PMC	Static "restart to finish uninstall" text + Restart → convert directly to a Fluent InfoBar.
PackageRestoreBar	PM UI + PMC	Split into two parts: Keep the static prompt as an InfoBar which becomes a Fluent InfoBar. "Some NuGet packages are missing from this solution. Click to restore from your online package sources. Restore"
		New Restore action moves to a reusable restore Task Status Center (TSC) notification (progress indicator & details). Delete in-bar progress bar, animation, copy menu.
LoadingStatusBar	PM UI: packages list	Error state → Fluent InfoBar. Loading spinner, pagination, per-source diagnostics stay inline.

Already removed

Bar	Reason	PR
ProductUpdateBar	Referenced from ConsoleContainer, but backing service is a stub that's unreachable at runtime.	Removed: NuGet/NuGet.Client#7547
PRMigratorBar	Unreferenced dead code.	Removed: NuGet/NuGet.Client#7528