zed: Fix formatting in workspace initialization (#22152)

This PR fixes some formatting issues in the workspace initialization
code that stemmed from certain constructs causing `rustfmt` to bail out
of the formatting.

The bulk of the content of `initialize_workspace` has been factored out
into functions, as having nested closures within closures seems to be
the primary cause of `rustfmt` being unhappy.

Release Notes:

- N/A