fix: add support for @* treesitter highlight groups

[myuwi]

nvim-treesitter recently dropped support for the TS* highlight groups (See: nvim-treesitter/nvim-treesitter#3656) which broke Treesitter support for many themes, including this one.

I have added the corresponding @* highlight groups which should return the syntax highlights back to normal. The old TS* highlight groups can likely be removed in the future, but I have kept them untouched for now in case they are needed for backwards compatibility with older Treesitter versions.

Edit: It seems like these changes aren't 100% in line with the previous highlight groups, so some changes need to be made before this can be merged. TODO tags, for example, aren't using the iris color anymore.

[myuwi]

I have rechecked the highlight groups and made some changes based on nvim-treesitter/nvim-treesitter@42ab95d and the Neovim Treesitter docs, and the highlight groups seem to be more in line with the previous ones now. I am still a little bit unsure if the groups are 100% correct, as I haven't been able to check everything, but they seem fine now.

[mvllow]

Thanks so much! Unable to test at the moment but will merge so people don't have a broken theme :)