refactor(terminal): introduce ITerminalLaunchResult interface

[bytemain]

The commit introduces a new interface ITerminalLaunchResult to replace the previously used inline return type { injectedArgs: string[] } in various terminal process-related methods.

When I want to add an attribute to the return type of start, I found that I have changed many files, so I want to add this pr first.

[Tyriar]

@bytemain I'm curious what you needed to add?

[bytemain]

@bytemain I'm curious what you needed to add?

need to know whether the shellIntegrationEnvironmentReporting is enabled for this terminal, because the logic at the node process will ultimately affect whether this feature is enabled, I need to obtain at the browser process whether the env reporting is finally enabled, so I modified the return type to { injectedArgs: string[], injectedEnv: Record<string, string> }.

But I think the code I mentioned above will not contribute to the VSCode repository.

[Tyriar]

Interesting. Note that the feature there is very much experimental and is likely to be tweaked. You probably don't want to depend upon it until the API is finalized tbh.