[API Proposal]: Compiled framework-dependent `.exe` should automatically download and install appropriate runtime

### Background and motivation

Hey,
So I come across a big problem that a lot of people I know complain about: Bundle size of self-contained executables.
These can reach upwards of 80 MB for a decently sized app, and that can be a huge problem, more bandwidth use, and entirely removes the benefit of having a shared system runtime that other apps can use.

My proposal is that the compiled framework-dependent executable includes an auto-installer for the runtime, as this would make my (example) 80 MB app just 15-20 MB.
AOT and trimming are not always an option, and I would much prefer a shared runtime as .NET is "intended" to be used.

### API Proposal

When the user starts the .net `.exe`, if the runtime is not installed, they should be met with a prompt to automatically install dependencies on the system

### API Usage

`none`

### Alternative Designs

_No response_

### Risks

_No response_