feat: add aria labels for connections

[maribethb]

The basics

• I validated my changes

The details

Resolves

Fixes #9794

Proposed Changes

• adds aria labels for rendered connections
• adds tests
• note i did not follow the design doc exactly because that resulted in suboptimal labels for value inputs. in the design doc, and in the screenreader experiment, value input connections would be labeled as "empty" unless the block also had a statement input. that didn't make sense to me so value inputs always get labels now.

for this block for example

according to the design doc, the label should be "Empty" instead of "if true"

that doesn't seem right so i just ignored that part

Reason for Changes

Test Coverage

added (ai-assisted) tests

Documentation

Additional Information