We can now return a DebugAdapterExecutable from provideDebugAdapter that will allow us to run out debug adapters out-of-process again, but still pick a different one based on project type:

https://github.com/Microsoft/vscode-docs/blob/vnext/release-notes/v1_28.md#debug-api-1
microsoft/vscode#59107

This will remove any possibility of us leaking memory in debug sessions that could affect the extension host and prevent us accidentally sharing state between the two (which we currently do, like with globalFlutterArgs).

• re-enable the lint in lints/disallowImportingNonSharedCodeRule.js when DAs run out-of-process