No way to use function parameters using touch interface in blocks

In CodeWorld blocks, if you're using a touch screen, you cannot drag parameters from the parent function block. Instead, you end up grabbing the entire function block.

Reproduce the issue in CodeWorld blocks using a touch screen, then trace the block interaction handling for dragging parameters from a parent function block. Done means a parameter can be dragged without selecting or moving the entire function block.

Written by the indexing model from the issue text.