GEOMETRY FIELD

This is a regression introduced by the fix for bug #21614368.

Problem: Queries that need to store the result of ST_AsBinary/ST_AsWKB
in a temporary table will fail with an error message.

Item_func_as_wkb::field_type() claims that the item returns a geometry
column, but actually returns a binary string (WKB).

Fix: Revert the fix for bug #21614368.

New fix for bug #21614368: Change Item_cache::setup() to copy the used
tables map from non-field items. This will make the Item_cache object
non-const during resolving, and example's val_xxx() won't be called.