[mu4e bug] The new mu4e-compose-new function does not return buffer name

[armindarvish]

Describe the bug
mu4e-compose-new used to return the name of the new buffer created. This was useful because then one could automate things when composing. But with the new approach using compose mail, the return value is some meaningless value that seems to do with minibuffer! It would be nice to restore the previous behavior to return the buffer that is created.

How to Reproduce
Run (setq testvar (mu4e-compose-new)) and see the return value for testvar.

Environment
MacOS, GNU Emacs 30.0.50, mu/mu4e 1.12.0

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