LP#1765444: improve how MARC editor fetches fixed field metadata

LP#1765444: improve how MARC editor fetches fixed field metadata

This patch fixes a problem where the web staff MARC editor would
make repeated and redundant calls to two Evergreen methods to fetch
data about fixed field positions and values if that metadata was
not already cached by local storage or Hatch.

In particular, this patch caches and returns the data retrieval
promises, ensuring that only one set of FF position and value
requests are made.

Prior to this patch, each eg-marc-edit-fixed-field directive, of which
there are 64, could end up invoking those methods when initializing
the editor for a record type that had not been previously seen.

To test
-------
[1] Clear all FFPosTable_* and FFValueTable_* keys from local storage
    (or Hatch).
[2] Retrieve a bib record in the web staff client. Note that up to
    64 calls each are made of open-ils.cat.biblio.fixed_field_values.by_rec_type
    and open-ils.fielder.cmfpm.atomic.
[3] Apply the patch and repeat steps #1 and #2.
[4] This time, note that only one call each are made.
[5] Verify that the fixed field inputs continue to work as expected.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>
Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Cesar Velez <cesar.velez@equinoxinitiative.org>