Use CallerFInfoFunctionCall with btree_gist for numeric types

Use CallerFInfoFunctionCall with btree_gist for numeric types

None of the existing types actually need to use this mechanism, but this
will allow support for enum types which will need it. A separate patch
will adjust the varlena types support for consistency.

Reviewed by Tom Lane and Anastasia Lubennikova

Discussion:  http://postgr.es/m/27220.1478360811@sss.pgh.pa.us