Use precompiled DEX files to speed builds

Our `_CompileToDalvik` task is currently the most expensive part of a user application build.

For example, for the following sample:

```
dotnet new android
dotnet add package Xamarin.AndroidX.Activity --version 1.9.3.1
```

This passes 34 dependency `.jar`s to the `_CompileToDalvik` task, which takes ~11.5s to execute on a DevBox.

[D8](https://developer.android.com/tools/d8) provides the ability to compile a library individually ahead of time. When the "final" compilation is done it only needs to copy over the DEX code rather than compile it.

```
android-toolchain\jdk-17\bin\java.exe
-Xmx1G
-classpath "C:\Program Files\dotnet\packs\Microsoft.Android.Sdk.Windows\35.0.7\tools\r8.jar"
com.android.tools.r8.D8
--debug
--min-api 24
--output "mono.android.24.dex"
"C:\Program Files\dotnet\packs\Microsoft.Android.Ref.35\35.0.7\ref\net9.0\mono.android.jar"
```

Precompiling the 34 dependency `.jar`s and using them reduces the "final" `_CompileToDalvik` invocation to ~5.2s. 🎉

### Wrinkles

The biggest wrinkle to this is that the output is different based on the `--min-sdk` that is passed in (particularly around desugaring), so we can't have a single precompiled DEX file. In theory we would need one per possible `min-sdk`, unless we can prove that we only need ones for API-21 and API-24. This makes it harder to ship precompiled binaries if we need to ship ~14 API levels.

Ideally, we could simply perform this compilation on first use and cache it, however it takes an extensive amount of time to precompile each `.jar` file. It takes about ~88s to precompile the 34 dependency `.jar`s used in the test above. This is a considerably longer "first compile" than not using caching at all.