Prevent empty nodes

[meck-gd]

This MR changes Get-AST so it doesn't create the sort of empty nodes that would be removed later on in optimization passes anyway. Most of those nodes should be (mostly, already are) attributes instead.

The resulting XMLs are up to 15% smaller, which can make a significant difference for multi-megabyte input scripts with AST node counts in the millions.

I've repurposed the opt_remove_empty_nodes pass to make malware2 look nicer instead - in combination with the new opt_remove_nested_statement_blocks.

[meck-gd]

@thewhiteninja Any comments on this? I know the MR diff looks obnoxiously huge, but that's mostly because of the data update. The first two commits should be much more reviewable individually.