Description of proposed changes

This implements the capability to have leading zeros on the geographical coordinates on the map frame, by extending the syntax for FORMAT_GEO_MAP and FORMAT_GEO_OUT to have:

• ddd for integer degrees
• DDD for fixed format integer degrees (3 digits of longitude, 2 digits for latitude)

Example:
gmt basemap -R-1/1/-1/1 -Baf --FORMAT_GEO_MAP=DDD:mm:ss -JM15c -pdf map

It also fixes what was effectively a bug (#7475). Longitudes are now properly written with 3 digits for the degrees in longitude.
Example:
echo 7.54353543 9.1342 | gmt convert -fg --FORMAT_GEO_OUT=DDD:mm.xxxF
now properly results in
007:32.612E 09:08.52N
while
echo 7.54353543 9.1342 | gmt convert -fg --FORMAT_GEO_OUT=ddd:mm.xxxF
now results (equivalently to maps) in
7:32.612E 9:08.52N

Fixes #7475

Reminders

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