Fix source build when using --no-build-js

[MackinnonBuck]

• Checks in blazor.webview.js
• Updates Microsoft.AspNetCore.App.Internal.Assets to build successfully when using --no-build-js, even when the framework JS assets are not on disk

Fixes #59114

[javiercn]

We only need --no-build-nodejs for source build, isn't that the case?

Can we not instead update the check so that in that situation just disable the check that triggers the error when we are running inside source build?

Source build doesn't run any code, it just builds it, and the JS assets are not needed for the build step.

[MackinnonBuck]

We only need --no-build-nodejs for source build, isn't that the case?

Can we not instead update the check so that in that situation just disable the check that triggers the error when we are running inside source build?

Source build doesn't run any code, it just builds it, and the JS assets are not needed for the build step.

Yeah, that sounds good. I'll update this PR to disable the check if not building with NodeJS.

Eventually I think we'll want to change blazor.webview.js to also not be an embedded resource and instead be included as part of M.A.A.Internal.Assets