Assistant: Provide a way to exclude some files from inline completions

[jmcphers]

Currently, Assistant provides inline completions everywhere:

positron/extensions/positron-assistant/src/extension.ts

Line 169 in a8bf9ce

const complDisp = vscode.languages.registerInlineCompletionItemProvider(ALL_DOCUMENTS_SELECTOR, completionProvider, { displayName: modelConfig.name });

This can be at best annoying but at worst a security concern (e.g. you don't want it autocompleting secrets, nor sending secrets as context to a third party).

There are two sides to this issue; one is excluding auto-completions from being shown to the user (e.g. as in github.copilot.enable for a set of file types), and the other is excluding the file's content from inclusion in the context sent to the model for privacy and security reasons.

https://docs.github.com/en/copilot/managing-copilot/configuring-and-auditing-content-exclusion/excluding-content-from-github-copilot#limitations

Positron should ship with exclusions pre-configured for typical data science projects files that contain secrets, such as .Renviron and .env files (for example).

[jthomasmock]

We should also have exclusions for hidden files/folders like .git, .venv, .ssh, as well as binary/data files, and some opinionated .dotfiles like .Rproj if we aren't already.

For example, in RStudio: https://github.com/rstudio/rstudio/blob/8e3a3124784eab15cc2dd51e088bb06481e03c04/src/cpp/session/modules/SessionCopilot.cpp#L249-L278

[timtmok]

There is a preference to add exclusion patterns for inline completion. This uses the glob pattern rules found in other settings and a link is provided in the description that explains how to create the glob pattern.

#8216 continues the work to exclude the files from the AI context so that excluded files aren't leaked when looking at the project files.

[rodrigosf672]

@jthomasmock @timtmok Note: when interacting directly with .env file, Assistant does reveal my secret. But it doesn't do so in line completions or if I add .env to the list of glob patterns. Is this expected behavior?

[timtmok]

@rodrigosf672 #8216 continues the work to exclude files from the context