chore: cover same-dir import map auto-import alias (#34645)

Adds LSP regression coverage for auto-import completions when an import
map alias points at the same directory as the referrer, such as `$src/`:
`./src/`. The test verifies that resolving the completion inserts the
import-map alias instead of regressing to only the relative path.

Also removes an unused HTTP test server fixture from the adjacent
passthrough import-map test so it does not depend on fixed test-server
ports.

Closes denoland/divybot#382

Co-authored-by: divybot <divybot@users.noreply.github.com>
Co-authored-by: Divy Srivastava <me@littledivy.com>