Manual roll is needed because incoming dart sdk requires updated version
vm_snapshot_analysis (>=0.7.4).


https://github.com/flutter/engine/compare/5ae09b8b4fa381e8723ed5382a26eafd0d97236f...7c83ea3e854202aea22405a947ac1b8f18c5a72c

```
7c83ea3e85 Reland "Manual roll Dart SDK from 2d98d9e27dae to 0b07debd5862 (21 revisions) (#43457)" (#43472)
9ef3e8d533 Roll Skia from 5eba922297bb to 93c92f97f5ab (2 revisions) (#43471)
```

Remove implementation of SuitePlatform from the test as well. Remove use
of fake cwd from SuitePlatform as it can't be properly faked.

* [flutter_tools] [dap] Add support for passing env variables to spawned processes

* Use named args

* Use in-memory fs and FakePlatform

* Pass filesystem style to MemoryFileSystem