Expose find_bounds publicly from mapl3g_OpenMP_Support (#4729)

find_bounds was imported from mapl3g_Subgrid but not listed in the
public statement, making it inaccessible to consumers such as
GEOSgwd_GridComp which is being migrated from MAPL_OpenMP_Support
(generic/) to mapl3g_OpenMP_Support (generic3g/).

Author: tclune

generic3g/OpenMP_Support.F90

@@ -15,6 +15,7 @@ module mapl3g_OpenMP_Support
 
     public :: Interval
     public :: make_subgrids
+    public :: find_bounds
     public :: make_subfields
     public :: make_subFieldBundles
     public :: make_substates