Make geometry cast functions error safe

Make geometry cast functions error safe

This adjusts cast functions of the geometry types to support soft
errors.  This requires refactoring of various helper functions to
support error contexts.  Also make the float8 to float4 cast error
safe.  It requires some of the same helper functions.

This is in preparation for a future feature where conversion errors in
casts can be caught.

(The function casting type circle to type polygon is not yet made error
safe, because it is an SQL language function.)

Author: jian he <jian.universality@gmail.com>
Reviewed-by: Amul Sul <sulamul@gmail.com>
Reviewed-by: Corey Huinker <corey.huinker@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/CADkLM%3Dfv1JfY4Ufa-jcwwNbjQixNViskQ8jZu3Tz_p656i_4hQ%40mail.gmail.com