[incremental models] add tests, various bugfixes and support for incremental predicates

[sdebruyn]

need to look at:

• correctly enable on_schema_change for incremental models #326
• Bug in incremental model: ('42000', "[42000] [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]Incorrect syntax near the keyword 'column'. (156) (SQLExecDirectW)") #217
• sqlserver__alter_column_type - Not working for column change #338
• Incremental model generates error in sql-server #261
• Incremental Strategy "Merge" is generating Delete, Insert into command #246
• Incremental Model Fails When Column Varchar Size Increases (Edge Case) #133

resolves #338
resolves #217
resolves #333
resolves #133
resolves #326