Complete string identifier parsing and add SERIAL_SEQUENCE function

The Strings.parseQualifiedName() added recently punted on dealing with quoting or casing. Properly handle those now.

It's unfortunate that we can't really delegate to the real parser but there (probably) aren't enough edge cases in this specific use case to make that really needed.

Update the SequenceValue function to use the new parser and add test cases to close the related card.

Lastly, add a SERIAL_SEQUENCE function for getting the sequence associated with a column.

There is similarity in the SerialValue, ColumnTypeString and SerialSequence evaluate implementations but not quite enough for me to add a base class. Though I could, if desired.