This patch defines `fir::SafeTempArrayCopyAttrInterface` and the
corresponding
OpenACC/OpenMP related attributes in FIR dialect. The actual
implementations
are just placeholders right now, and array repacking becomes a no-op
if `-fopenacc/-fopenmp` is used for the compilation.

Added options:
  * -f[no-]repack-arrays
  * -f[no-]stack-repack-arrays
  * -frepack-arrays-contiguity=whole/innermost

This change enables LoopVersioning when `fir.pack_array` is met
in the def-use chain. It fixes a couple of huge performance regressions
caused by enabling `-frepack-arrays`.

TARGET dummy arrays can be accessed indirectly, so it is unsafe
to repack them.
INTENT(OUT) dummy arrays that require finalization on entry
to their subroutine must be copied-in by `fir.pack_arrays`.

In addition, based on my testing results, I think it will be useful
to document that `LOC` and `IS_CONTIGUOUS` will have different values
for the repacked arrays. I still need to decide where to document
this, so just added a note in the design doc for the time being.

This API will be used for copying non-contiguous arrays
into contiguous temporaries to support `-frepack-arrays`.
The builder factory API will be used in the following commits.

This is a document describing why and how to add support for repacking
of assumed-shape dummy arrrays to provide more efficient data cache.
It proposes adding new FIR operations and outlines the compiler flow
handling these operations.
I would like to hear feedback on all of it, but especially on:
  * The possibility of detecting safeness of the repacking
    in the context of OpenACC/OpenMP. If it is not possible
    to do the runtime checks to determine safety, then
    there is not need to add the `TempCopyIsSafe` attributes
    to the instruction.
  * Whether it is possible to preserve the debug information
    in cases where `fir.pack_array` is sunk after `[hl]fir.declare`,
    so that before the `fir.pack_array` a debugger will refer
    to the values in the original array, and after `fir.pack_array`
    it will refer to the copy.