windows-reactor inline bootstrap for framework-dependent apps

[Rafael Rivera (riverar)]

This PR adds a new way to run framework-dependent apps: instead of needing a bootstrap DLL, the app now resolves and loads the Windows App Runtime framework package directly at startup. That means a cleaner dev experience (no build scripts needed for framework-dependent apps) and a smaller on-disk footprint (no additional DLL).

[Kenny Kerr (kennykerr)]

In #4848, App changed materially - it is now a stateless launcher, while title, sizing, visuals, and other settings are owned reactively by each window's root component. This supports multi-window apps better, so restoring the old App builder would work against the new architecture.

For #4847, I suggest porting the direct package-resolution logic into the new centralized bootstrap_runtime() path rather than carrying over App::framework_dependent(). Builds without the self-contained marker can automatically use the framework-dependent path. The feature is still a good fit, but I think we should land #4848 and then port this with bindings regenerated from the new generator rather than resolving the old branch's many mechanical conflicts.

[Rafael Rivera (riverar)]

Kenny Kerr (@kennykerr) Sounds good, will port to #4848