* Use CSProj for packing Platforms package

* Port GenerateRuntimeGraph task

This ports the GenerateRuntimeGraph task from arcade as of
https://github.com/dotnet/arcade/tree/d005a8ce6bb81129f9c3a4a907e1b7ccbf2504d5

* Refactor GenerateRuntimeGraph into separate files

* Add test for GenerateRuntimeGraph

* Fix up path to runtime.json

* Don't filter inner builds when building Platforms task

* Skip tests RuntimeGraph task tests on some platforms

* Exclude browser from testing instead of wasm

* Another try at suppressing testing on Browser