Followups from the new C++/WinRT

[DHowett]

Interesting things we could do after #14869 landed:

### Tasks
- [x] remove all `InitializeComponent` calls - they do it automatically
- [ ] use `std::optional`<->`IReference` automatic binding
- [x] use `std::format` support (!) for json/uri/hostname/http stuff/all `IStringable`s
- [ ] potentially move to `/await:strict` for C++20 coroutines

[DHowett]

We should probably not upset the delicate balance of InitializeComponent calls, because removing them can make it so that XAML things we reference from the ctor break.

The only ones of these that really have legs are:

• optional <-> IReference binding
• await:strict

I checked the others off after an audit.