Add a _update_multi_column_transformer method

[R-Palazzo]

Problem Description

Currently, when a user calls update_transformers, he can modify any column to transformer mapping, including multi-column transformer. In this case, these changes can cause some multi-column transformers not to work (for instance, when they no longer have enough columns in their tuple).

Expected behavior

A _update_multi_column_transformer should be added to check that the new mappings are valid for the multi-columns.
For each multi-column, this method should:

• Create a columns_to_sdtype dict based on the tuple of column
• Validate the transformer by calling its _validate_sdtype() in a try/catch
• If didn't crash, this means the config is valid.
• If it crashes, the multi-column should be removed and each column should be assigned to its default transformer per sdtype. Also, a warning should be raised saying:

Userwarning: "Transformer 'RandomlocationGenerator' is incompatible with the multi-column field 'A'. Assigning default transformer to the columns."

• Update the _multi_column_fields

Finally, this method should be called at the end of:

• update_transformers
• remove_transformers
• remove_transformers_by_sdtype
• update_sdtypes