Logical schema exposed to engine should not include column mapping metadata

[scovich]

Describe the bug

Column mapping field metadata is an internal Delta detail and unsuspecting engines should not be exposed to it as the metadata could propagate in unwanted ways (such as from source to target as part of a CTAS).

To Reproduce

Create a column mapped table. Snapshot::schema includes column mapping metadata.

Expected behavior

It should not.

Additional context

No response