Workflow Editor: Replace instead of recreate terminal on update.

This fixes at least one subtle bug related to multiple input data parameters (actually probably two bugs) because the old logic assumed there was only one connector per input terminal.

This should be more efficient, lead to some code duplication deletion in subsequent changesets, and really help dataset collections where terminals are much more complex (there are data inputs and collection inputs, and each can be mapped over by collections) - this helps manage complexity downstream.
Workflow Editor: Merge addDataInput and replaceDataInput into common method.

Reduces some code duplication here and reduces even more code duplication downstream in dataset collections work.