Use Fallback Chunking for Unsupported Languages / Extensions for Codebase Indexing

[adamhill]

A few people have been asking about CBI issues resulting from the language not being supported by the tree-sitter grammars that Kilocode includes.

There is a Roo PR that has added a mechanism to use the fallback chunking mechanism if we dont have a tree-sitter grammar for it. Currenlty it is hard-coded for .vb and .scala extensions.

It would be useful to expose a simple UI for having an exposed list of extensions (*.xxx) style that will always use the fallback chunking. One of the most common project type we dont support is Flutter with *.dart files, in the past it has caused actual hangs and Extension reboots.