Support error_data (new in 1.4.0)

[jraymakers]

It seems that the "error" functions that return a string are being replaced with "error_data" functions that return a structured error object.

New type: duckdb_error_data
New functions:

• duckdb_create_error_data
• duckdb_destroy_error_data
• duckdb_error_data_error_type
• duckdb_error_data_message
• duckdb_error_data_has_error

Currently, the only usage of this new mechanism is in the appender, where duckdb_appender_error_data replaces the (now deprecated) duckdb_appender_error function.