Replace variables using slash commands

[SDGLBL]

Currently, there is an issue with #buffer #buffers #lsp where users cannot see the specific content represented by these symbols after introducing these commands, nor can they modify this content. Referring to zed, I think we can use nvim-cmp to introduce a similar slash command that allows users to quickly bring context into the chat buffer using /cmd args. This actually eliminates the complex variable replacement mechanism in chat implementation and feels more intuitive overall. At present, I have implemented an initial version of this feature through nvim-cmp, and it works very smoothly.

[olimorris]

You technically can see it if you open up debug mode in the chat buffer with gd. But yep it's very clunky right now. But this will be better once I push the messages refactor through later this weekend.

[olimorris]

Could you share this in a PR? This looks awesome

[SDGLBL]

@olimorris #119