Ruby: support HAML template files

[MaxSchlueter]

It would be nice if CodeQL supported extraction of HAML template files into the database, like it does for ERB template files. One challenge here is that there is no existing tree-sitter grammar for HAML yet, unlike for ERB template files, making it more difficult to integrate with the extractor. Tree-sitter grammar support for HAML has also come up elsewhere: zed-industries/extensions#179

[jketema]

@MaxSchlueter Thanks for the suggestion. We'll take this in consideration.