In languages that uses "{" for blocks, accepting a Copilot completion
that ends with "{", causing a structural imbalance, which
structural-based packages like smartparens does not like and causes
headaches.
With the custom accept function, trailing "{" chars along with any
whitespace before it, are ignored from Copilot completion. An exception
is made for if the removal of trailing "{" and whitespace yields an
empty completion, in which case the completion is accepted as is.
Previously we only hide company-mode's in-line preview when there was
only a single result. This meant that it didn't show the one result
anywhere.
This allows company-mode to still show it's regular popup even when
there's only one result.
I opted for accepting copilot completions using C-<tab> /
<backtab> (shift+tab) instead of regular tab, as it was often getting in
the way of yasnippet and lsp completion suggestions. This allows a more
explicit acceptance of Copilot suggestions.
