Incorrect highlighting dragging when there's no trailing line

[microbit-matt-hillsdon]

[microbit-matt-hillsdon]

This is still the case after recent drag and drop changes.

[microbit-matt-hillsdon]

There's a related issue where we don't get the indent right when dragging into an empty block at the end of the document. Similarly to this, we don't account for the fact the insertion may begin at the end of the preceding line. Different but similar fix.

[microbit-matt-hillsdon]

There's a related issue where we don't get the indent right when dragging into an empty block at the end of the document. Similarly to this, we don't account for the fact the insertion may begin at the end of the preceding line. Different but similar fix.

This is now fixed on the PR captured by the edits.test.ts "uses correct preceding line for indent at end of document" test.