[dev_compiler] Remove fileUri from LibraryMetadata

[annagrin]

Remove fileUri from LibraryMetadata as it is not used and also introduces local paths into metadata.

Note

This is a breaking change, so the clients need to be prepared before this change is made:

• dwds: add support for reading two metadata versions
• webdev: update to the dwds version above
• flutter: update to the dwds version above.
• finally, update metadata in the SDK:

https://dart-review.googlesource.com/c/sdk/+/163123