This reverts commit 275ab9c6.

Revert "Reland "Remove references to Observatory (#118577)""

This reverts commit 298d8c76.

This reverts commit 2df140f4.

Observatory is being deprecated for Dart 3.0 so it should no longer be
referenced in tooling messaging / flags.

See https://github.com/dart-lang/sdk/issues/50233

[flutter_tools/dap] Add a base Flutter adapter class to avoid duplication between adapters (#114533)

[flutter_tools/dap] Map org-dartlang-sdk URIs to the location of the source files found by the analyzer (#114369)

Since https://github.com/dart-lang/sdk/commit/02d9c3e6a586ad47909262931375f25abb34b4e3 this flag does absolutely nothing. The behaviour it controlled is now automatic and the flag is not required.

The flag will be removed from the Dart SDK in the future after Flutter is no longer using it.

Provide more useful error message if a non-compliant DAP tool (or user) sends bad input to DAP server (#107827)

* [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

* Fix issues running integration tests through DAP

These adapters were incorrectly trying to connect a DDS instance even when Flutter would create its own. This change disables DDS in the DAP layer and leaves it to Flutter (although it passes `--no-dds` on to Flutter if provided to the DAP process).

Also fixes an issue where we would unnecessarily connect the VM Service for tests even in 'noDebug' mode because of a change/fix that now includes a 'vmServiceUri' in the `test.startedProcess` event.

* Add support for running tests through debug-adapter

* Improve comments about stdout + remove pedantic