Database: decrease db size by using a INTEGER_OR_TEXT data type on codes

Most codes (especially *all* in EPSG) are integers. As integers are
stored as variable-length in the db, it is preferable to store them as
such when possible.

So use a special INTEGER_OR_TEXT data type. This is a
"non-standard" type declaration, but this is perfectly legal as SQLite is
loosely typed.

As this declaration contains the string INT, it is assigned INTEGER affinity.
Which means that values provided either as text (that contains integer value)
or integer will be stored as integers, whereas text values will be stored as
text. See paragraph 3 and 3.1 of https://www.sqlite.org/datatype3.html.
The "INTEGER_OR_TEXT" name is a hint for the user, and software like
GDAL (>= 3.3) to expose the column as string...

The effect of using this rather than TEXT is making the DB size go from
9 MB to 8.4.

There is no need to change the DATABASE.LAYOUT version numbering as this
is completely forward and backward compatible.

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