Add support for controlling the "compat" app icon shape

### Description

In Android 8.0 (API 26), the OS added support for adaptive icons. Resizetizer handles this just fine, however when it generates the backwards compat icon, it is just a square - or more specifically it is just drawing the background as is.

The Android 8.0 OS has some options:


But for older version of the OS, the developer is responsible for generating the "shape". For example, in Android Studio:


As you can see, there is both a round icon and a legacy icon. We already have the round *adaptive* icon, but still need to add the legacy versions of both the actual round image and then the shaped image (square - current, squircle, rounded square, circle)

There is also an app that can be used to test many variations: https://github.com/nickbutcher/AdaptiveIconPlayground

In summary, we have:

* [x] Adaptive shaped
* [x] Adaptive round
* [x] Legacy none

We are missing:

* [ ] Legacy round
* [ ] Legacy shaped (square, squircle, circle, rounded square)
* [ ] Legacy alternate shaped (vertical, horizontal)

### Public API Changes

Maybe all we need is an optional parameter on ``

This would then be a choice of a few things:

* None (current and default)
* Square
* Circle
* Rounded Square
* Squircle
* Vertical
* Horizontal

### Intended Use-Case

More things to support typical scenarios.

Start by tracing the Resizetizer path that generates backward-compatible icons and review how the MauiIcon Shape API is defined. Compare the current legacy output with the requested round, shaped, and alternate-shaped variants; done means the supported choices generate the corresponding legacy icons while preserving the current default.

Written by the indexing model from the issue text.