…olution

When pj_obj_create() exports a coordinate operation to a PROJ string, it
previously passed nullptr as the database context to PROJStringFormatter.
This prevented substitutePROJAlternativeGridNames() from resolving grid
names via the grid_alternatives table.

For grid transformations where old_proj_grid_name is NULL (153 entries in
the standard PROJ database), the file-level fallback (getProjGridName)
cannot resolve the grid because it queries old_proj_grid_name. Only
lookForGridAlternative (which queries original_grid_name) can resolve
these grids, but it requires a database context.

This change adds getDatabaseContextIfOpen() to projCppContext, which
returns the cached database context if already opened (e.g. from a prior
proj_create_from_database call), without attempting to open proj.db.
This preserves the original intent of commit 63c491e that callers
using plain pipeline strings can run without proj.db.

Adds a test for EPSG:9484 (grid href2008a.bin -> no_kv_href2008a.tif)
which has a NULL old_proj_grid_name.