feat: make cacheAllConnectionPairs public

[mikeharv]

The basics

• I validated my changes

The details

Resolves

Fixes RaspberryPiFoundation/blockly-samples#2708 (Requires plugin update as well)

Proposed Changes

• Make BlockDragStrategy.cacheAllConnectionPairs() public so consumers can refresh the cached connection pairs during an active drag.
• Call this method for all types of block drag, not just keyboard-driven

Reason for Changes

BlockDragStrategy caches valid connection pairs when a drag begins. If another block changes shape during the drag, such as a plugin dynamically adds an input, the cache does not contain the new connection. This is required to make @blockly/block-dynamic-connection work correctly with keyboard move mode.

Cached connections are also necessary for ensuring properly verbose move mode announcements (e.g. disambiguating similar connections on a neighbour), but this information was missing for pointer drags.

Test Coverage

Added Mocha tests:

• Confirm recaching adds the new connection and that it wasn't there previously.
• Confirm constrained traversal visits the existing input followed by the newly added input in the expected order.

Documentation

Additional Information

See RaspberryPiFoundation/blockly-samples#2751 for corresponding plugin change.