[flang] Restructure runtime to avoid recursion (relanding) (#143993)

Recursion, both direct and indirect, prevents accurate stack size
calculation at link time for GPU device code. Restructure these
recursive (often mutually so) routines in the Fortran runtime with new
implementations based on an iterative work queue with
suspendable/resumable work tickets: Assign, Initialize, initializeClone,
Finalize, and Destroy.

Default derived type I/O is also recursive, but already disabled. It can
be added to this new framework later if the overall approach succeeds.

Note that derived type FINAL subroutine calls, defined assignments, and
defined I/O procedures all perform callbacks into user code, which may
well reenter the runtime library. This kind of recursion is not handled
by this change, although it may be possible to do so in the future using
thread-local work queues.

(Relanding this patch after reverting initial attempt due to some test
failures that needed some time to analyze and fix.)

Fixes https://github.com/llvm/llvm-project/issues/142481.

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