fix(ts-highlighting): get hl name from the capture (#1166)

After this commit (https://github.com/neovim/neovim/commit/2460f0a7028550ea2d87492a4e8b95914fdba7b1), the `hl_cache` variable
stores the hl_ID instead of the group name.

Another way to get the hl name which is adopted from the method used
here `_get_hl_from_capture`:

    ```lua
    local hl = vim.treesitter.highlighter.hl_map[query.captures[id]]
    ```

But, as the method covers another case, we can directly use it.

I've also added the type guard so that, in the future, it does not
explode like it does now.

fixes: #1151

0 files changed, 0 insertions, 0 deletions