This PR updates the file icon mappings such that:

- C# (`.cs`) files map to the `csharp` key
- Cue (`.cue`) files map to the `cue` key
- GitLab YAML (`gitlab-ci.yml`) files map to the `gitlab` key
- Luau (`.luau`) files map to the `luau` key
- Solidity (`.sol`) files map to the `solidity` key

Release Notes:

- Icon themes: Added the ability to change the file icon for C# (`.cs`)
files.
- Icon themes: Added the ability to change the file icon for Cue
(`.cue`) files.
- Icon themes: Added the ability to change the file icon for GitLab YAML
(`gitlab-ci.yml`) files.
- Icon themes: Added the ability to change the file icon for Luau
(`.luau`) files.
- Icon themes: Added the ability to change the file icon for Solidity
(`.sol`) files.

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Co-authored-by: Marshall Bowers <git@maxdeviant.com>