Runtime: Add helper function for accessing bundled resource bundles

[stackotter]

Resource bundles get placed at a different relative path depending on the platform, and to complicate things further, Swift Bundler users can't use Bundle.module or similar accessors because SwiftPM hardcodes absolute resource bundle paths and then crashes when it can't locate the bundles.

To solve this, we'll likely have to embed the relative path to the resource bundle directory as a metadata property that the runtime can read.

[stackotter]

Once resolved, we should also document that Bundle.module will cause crashes when an app is distributed to another machine, and point users to use this instead.

We should also add a troubleshooting section for App crashes on Windows with no additional info, and explain that it could be a result of using Bundle.module, cause on Windows it results in a pretty silent crash.