collect Block Production
fun collectBlockProduction(flavour: MarkdownFlavourDescriptor, root: IElementType, text: CharSequence, productionHolder: ProductionHolder, cancellationToken: CancellationToken): List<MarkerBlock>
Fills productionHolder with the blocks of text, and returns the blocks that are still open at the end of text. The step finds the block boundaries only. It builds no ASTNode, and it parses no inline content.