Use `vscode-vfs` (instead of `gitlab-web-ide`) as Web IDE file system scheme

Description

Identified in this thread:

Update the Web IDE file scheme to vscode-vfs (from gitlab-web-ide). It looks like this is a hardcoded scheme in a number of VSCode logic (and even extensions). Without this, we're tripping on isTrustedVirtualResource always being true so the Web IDE context will always be trusted.

VSCode has some built-in logic which suggests that the main virtual file system used in the browser should be vscode-vfs. This blocks us from using enableWorkspaceTrust: true (see thread for more details ☝️).

Acceptance Criteria

• We've added a reference to vscode-vfs in the gitlab-vscode-extension project (see investigation notes)
  • Please make sure that it's safe to do this cross-project renaming across releases. We might need to do a two-step rename (one MR to add vscode-vfs, then release, then update everything, then remove gitlab-web-ide)
• We've replaced references to gitlab-web-ide file system with vscode-vfs (see investigation notes)
• We've tested and investigated enough to ensure that this change won't cause any issues...

Investigation notes

• There's a bit of references in the gitlab-web-ide project to this file system name:
  • In vscode-bootstrap we'll reference this as the "workspace" url https://gitlab.com/gitlab-org/gitlab-web-ide/-/blob/62d13a6d6c5ed664e06959e25060cf2de9c93a82/packages/vscode-bootstrap/src/start.ts#L293
  • In vscode-extension-web-ide this is referenced in the vscode.package.json and in the constants.ts.
  • There might be other references... Searching through all gitlab-web-ide would be a good start. Unfortunately, we use this string a lot.
• There's also references in the vscode-extension to this file scheme:
  • https://gitlab.com/gitlab-org/gitlab-vscode-extension/-/blob/d5a2f0d13fe68352443bd7b0240bea181b723f33/src/common/code_suggestions/code_suggestions.ts#L54
  • https://gitlab.com/gitlab-org/gitlab-vscode-extension/-/blob/d5a2f0d13fe68352443bd7b0240bea181b723f33/src/common/language_server/register_language_server.ts#L40

Why doesn't the Web IDE use file: as the FS scheme?

I think the decision to avoid file: was made our of an abundance of caution. It's not clear how VSCode will interpret it's environment if this file scheme is present. Also, github.dev doesn't do this.

These concerns might be unfounded, but it would take some investigation to ensure the this is safe.