Clarify which input a block is being moved into

[gonfunko]

Currently, when a block is in constrained move mode, potential destinations are identified by reading out the proposed-parent block's label. In cases where the parent block has multiple (value or statement) inputs however, the input in question is not identified, which makes it challenging to place blocks. This should be improved, perhaps by using the field row label, index of the input or another method.

[BenHenning]

From @microbit-robert:

This is specifically a move mode issue, where it's not clear at the moment which branch of an if statement you are moving a block into. I can provide a diff of what I've done here shortly.

These are the changes we've made for move mode for user testing in isolation which includes handling the specific branch for if / else blocks https://github.com/RaspberryPiFoundation/blockly/compare/add-screen-reader-support-experimental...microbit-matt-hillsdon:blockly:move-mode-changes

This actually works better for MakeCode's if blocks than the Blockly test page if blocks. As the MakeCode blocks don't have the "do" text preceding the statement inputs, we use the text on the previous row. In the Blockly test page case, all 'else if' statements are labelled as "do", which can still be confusing.

[joreneng]

Adding a note that this was also a pain point with all of the user testers in this testing round.

[jversloot]

This was also an issue in our user tests with users moving their focus into a block and onto number inputs, and only being read out the value of the number, and not a title of what field they are focused on. Not sure if this is the same issue as when in move mode so I wanted to bring it up but can log it separately if it is different.

[maribethb]

Also relevant to #9686