g.proj: Add JSON support

[NishantBansal2003]

ref: #4104

This pull request integrates to add JSON output support to the g.proj module. With these changes, g.proj now supports output in JSON format when invoked with the -p flag.

The behaviour is as follows:

{
    "name": "Lambert Conformal Conic",
    "proj": "lcc",
    "datum": "nad83",
    "a": "6378137.0",
    "es": "0.006694380022900787",
    "lat_1": "36.16666666666666",
    "lat_2": "34.33333333333334",
    "lat_0": "33.75",
    "lon_0": "-79",
    "x_0": "609601.22",
    "y_0": "0",
    "no_defs": "defined",
    "unit": "Meter",
    "units": "Meters",
    "meters": "1"
}

NOTES: The code changes are largely based on the modifications introduced in #4104 with additional tweaks to address all review comments.

[NishantBansal2003]

Could we re-run this CI? The error does not seem to be related.

Errors in:
/d/a/grass/grass/lib/db/dbmi_driver
/d/a/grass/grass/db/drivers/sqlite
/d/a/grass/grass/db/drivers/postgres
/d/a/grass/grass/db/drivers/dbf
/d/a/grass/grass/db/drivers/ogr
/d/a/grass/grass/db/drivers/odbc

[NishantBansal2003]

@petrasovaa, Could you please review this PR when you have a moment? pinging in case it was missed.

[petrasovaa]

After discussing this with @wenzeslaus, we suggest adding the WKT (-w), proj4 (-j) and shell (-g) into the format option:
options: plain,shell,json,wkt,proj4
The -p flag would stay, but would just mean "Print projection information".
The flags would need to keep working for backwards compatibility, but should print a warning to use the format option instead.

Sorry for more changes again, but I think this will make more sense.

[NishantBansal2003]

we suggest adding the WKT (-w), proj4 (-j) and shell (-g) into the format option:
options: plain,shell,json,wkt,proj4

Should I remove the JSON format for the -w and -j flags, or should I use format->multiple = YES to provide multiple outputs, such as WKT and JSON or PROJ4 and JSON?

The -p flag would stay, but would just mean "Print projection information".

Should format=plain,shell,json be used with the -p flag, or should they be used independently?

[petrasovaa]

we suggest adding the WKT (-w), proj4 (-j) and shell (-g) into the format option:
options: plain,shell,json,wkt,proj4

Should I remove the JSON format for the -w and -j flags, or should I use format->multiple = YES to provide multiple outputs, such as WKT and JSON or PROJ4 and JSON?

Good questions. I meant removing the JSON. I wouldn't do multiple outputs.

The -p flag would stay, but would just mean "Print projection information".

Should format=plain,shell,json be used with the -p flag, or should they be used independently?

Without -p there should be no printing, so e.g. g.proj format=json would probably fail with "at least one of the options... need to be specified". (The other flags will still work for backward compatibility). Hope this makes sense.

[petrasovaa]

Just some small suggestions, looks great!