Parallelize project initialization tasks

Background

When a new project (created via the project wizard) is being initialized, a series of tasks is run to set up things like: initializing the project directory as a git repo, creating an environment for the project, creating empty files, etc..

Currently, we've ordered the tasks in a sequence that prioritizes the shorter tasks first, to provide the user with some sense of progress. If the longer tasks ran first, it could seem like nothing was occurring. https://github.com/posit-dev/positron/issues/3293 covers showing a notification that clearly indicates the project initialization progress.

https://github.com/posit-dev/positron/blob/93ad6f239fe5ddbbfe1ae8013d2ab61fb0b3417d/src/vs/workbench/services/positronNewProject/common/positronNewProjectService.ts#L160-L186

Proposal

It would be nice to try to run the steps concurrently when possible, to reduce the amount of time project initialization takes. A user should be able to jump into their new project promptly. In particular, creating an environment takes several seconds, so it would be ideal if we can start that task as soon as possible, while also running some quicker tasks at the same time.

This should coordinate with https://github.com/posit-dev/positron/issues/3293 appropriately. Running tasks concurrently may trigger multiple notification toasts at the same, which could be overwhelming.

Start by reading src/vs/workbench/services/positronNewProject/common/positronNewProjectService.ts around lines 160-186 to understand the current initialization sequence. Review issue 3293 for the related progress notification work. Done means compatible tasks can run concurrently, the environment starts earlier, and concurrent notifications are coordinated so they do not overwhelm users.