CASSANDRA-18714 5.0 squashed SAI indexes for CQLSSTableWriter

[smiklosovic]

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[smiklosovic]

add exception message

[maedhroz]

Suggested change

	private Supplier<CQLSSTableWriter.Builder> defaultBuilderSupplier = () -> CQLSSTableWriter.builder().removeSchemaAfterDone(false);
	private final Supplier<CQLSSTableWriter.Builder> defaultBuilderSupplier = () -> CQLSSTableWriter.builder().removeSchemaAfterDone(false);

[maedhroz]

Overall, LGTM

The only thing I'm not entirely sure of is whether we want the complexity of tracking currentTables outside the already existing static Schema state. Given the usage pattern of sequentially creating writers within the same JVM, we might consider an alternative where we just, rather than specifying removeSchemaAfterDone, tell the writer builder whether we want to overwrite existing/conflicting schema.