[NativeAOT-LLVM] Add sample & package testing

[SingleAccretion]

1. Add a BuildOnly project to the WASM runtime tests.
2. Configure it to publish (no need to run) the sample projects in two configurations:
   • With the 'official' experimental feed - this will test the already published packages.
   • With the local packages.

Perhaps also configure the project to be CI-only by default so that local testing with ./src/tests/build && ./src/tests/build doesn't need the packages to be built?