would like to configure the location of the client.js resource or provide bytes directly

Currently the client.js file is loaded using Isolate.resolvePackageUri. This mostly works for flutter, since we correctly provide a --packages file during snapshot creation. nevertheless, there are several edge cases where it will not correctly resolve the file:

* User downloads precompiled snapshot from website, but doesn't use bundled cache
* User creates a snapshot, but deletes/moves pub cache after wards.
* Probably something else I'm forgetting

These aren't incredibly common, but from the tool side of things there's not a lot we can do once a a snapshot is created. Instead it would be ideal if the tool could look up the client.js script itself and provide the bytes to dwds.start.

https://github.com/flutter/flutter/issues/58110

Start by tracing how client.js is loaded through Isolate.resolvePackageUri and passed to dwds.start. Define the supported configuration or byte-input path so snapshots still work when the bundled cache is absent or the pub cache has moved; done means the tool can supply client.js independently of that cache.

Written by the indexing model from the issue text.