Guidance on pattern to improve context for completions in an IDE

## Background

Our IDE has an opt-in feature where it will tell copilot about all files in the current project by doing `textDocument/didOpen` on them. This could potentially be dozens, possibly even hundreds of files, given the nature of the projects in real-world use.

This was originally implemented using the vim copilot plugin, now switched to using `copilot-language-server`.

## Question

Is this a "Good Idea"? Will it actually improve completion suggestions by providing more context, or will it quickly hit some internal limit?

When I switched this to `copilot-language-server` I also implemented setting `workspaceFolders` to true, and pass the root folder of the project as the workspace folder; is that accomplishing anything in terms of improving awareness of other files in the project (i.e. does this make the "pretend to open all files" approach redundant)?

Thanks!

Review the vim copilot plugin behavior, the switch to copilot-language-server, and the workspaceFolders and textDocument/didOpen handling described in the issue. Determine whether opening every project file improves completion context or reaches limits, then document the recommended pattern and whether workspaceFolders makes that approach redundant.

Written by the indexing model from the issue text.