Problem: Treesitter queries for a given language in runtime were merged together,
leading to errors if they targeted different parser versions (e.g., bundled viml queries
and those shipped by nvim-treesitter).
Solution: Runtime queries now work as follows:
* The last query in the rtp without `; extends` in the header will be used as the base query
* All queries (without a specific order) with `; extends` are concatenated with the base query
BREAKING CHANGE: queries need to be updated if they are meant to extend other queries