Problem:
Diagnostic highlight groups were applied by iterating and calling
`vim.hl.range` for each group individually. That resulted in multiple
extmarks with the same priority being created separately, which does not
allow `DiagnosticUnnecessary` and `DiagnosticDeprecated` with matching
options override `Diagnostic*` styling.
Solution:
Pass the list of hl-groups to `vim.hl.range` so they are applied
together in the correct order.
738cd366f9
