Properly pass nested script arguments for tasks (#10776)

Closes
https://github.com/zed-industries/zed/discussions/10732#discussion-6524347
introduced by https://github.com/zed-industries/zed/pull/10548 while
keeping both Python and Bash run selection capabilities.

Also replaced redundant `SpawnTask` struct with `SpawnInTerminal` that
has identical fields.

Release Notes:

- Fixed incorrect task escaping of nested script arguments

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Co-authored-by: Piotr Osiewicz <piotr@zed.dev>