Adds `-u`/`--unit-id-debug-info` arguments to `flutter symbolize` to pass paths to DWARF information for deferred loading units. The argument passed via `-u` should be of the form `N:P`, where `N` is the loading unit ID (an integer) and `P` is the path to the debug information for loading unit `N`. The DWARF information for the root loading unit can either be passed by `-d`/`--debug-info` as before or by `--unit-id-debug-info 1:<path>`.
Partial fix for https://github.com/flutter/flutter/issues/137527. Additional work is needed to adjust tools built on top of `flutter symbolize` to store and pass along this additional information appropriately when there are deferred loading units.
To avoid analyzer warnings when utf8.encode() will return the more
precise Uint8List type, we use const Utf8Encoder().convert() which
already returns Uint8List
See https://github.com/dart-lang/sdk/issues/52801
This class is entirely superseded by the application package factory. Only drive and install use it, and removing it from drive will allow use-application-binary support.
