.. to the targets.

- New property: `NativeAssets`, populated by `@(WasmNativeAsset)`
- Remove property `MicrosoftNetCoreAppRuntimePackRidDir`
- Also, add the `icudt.dat` file from the targets

WasmAppBuilder has (non-obvious) logic to:

1. if AOT'ing, then use the *generated* dotnet.{js,wasm};
2. else use the one from the runtime pack

This depends on Publish having copied those files from the runtime pack
to the publish directory, and then comparing paths in the builder to
decide which one to use.

Instead, make this the intention obvious, and clear.

We were getting these from the publish directory, instead we can get
them directly from the runtime pack.

This includes icudt.dt, and dotnet.timezones.blat .

.. where we can emit the generated native files. Since these files are
meant only for generating the final `dotnet.wasm`, we don't want them to
put them in the bin directory.

.. instead of trying to find them in the build dir. This build directory
will become a directory for intermediate build output in upcoming
commits.

- Instead of having a special $(WasmMainAssemblyPath), and then adding
  it to the wasm assemblies ourselves
  - let the user project add all the relevant assemblies to
    `@(WasmAssembliesToBundle)`, which is usually as simple as
    `$(OutDir)\*.dll`.

- This helps to simplify lot of things.
- And we just need the main assembly filename for generating the
  run-v8.sh script.

Based on the changes in previous commits, we can now remove
`$(WasmBuildDir)`, and replace that with an internal
`$(_WasmIntermediateOutputPath)`. This path will have all the build
artifacts generated that aren't required in the app bundle.

Earlier, we were using the publish directory for that, which resulted in
it being littered with unncessary files, and files getting copied to the
app bundle from unclear sources, and for non-obvious reasons.

… correctly reflect the value