Add a new source parameter: `snippetIndicator`

[110y]

What

• Add the snippetIndicator parameter to change the indicator string for snippet completion candidates.

Why

With recent (huge 👏) updates, now ddc-source-nvim-lsp adds an indicator string: ~, to snippet completion candidates. While it should work well for the majority of users, I think there might be a user who wants to change this string (in my case, I just want to remove ~).

Given that, this PR adds a new source parameter named snippetIndicator that enables us to change the indicator string for snippet completion candidates to an arbitrary string (including an empty string).

[uga-rosa]

deno task pre-commit is available to perform the local equivalent of a CI check.

[110y]

Thank you for your review! Let me fix it...

[110y]

@Shougo @uga-rosa

Sorry for the delay, I just handled all of your review comments. I appreciate it if you could take another look 🙏

[uga-rosa]

@Shougo please re-check

[110y]

Thanks a lot!