Fix support for inmemory files in did_open

[austin3dickey]

I didn't make an issue for this, but I can first if you'd like!

Summary

One-line change to fix inmemory documents (e.g. the Positron Console) failing to be registered with the server on Windows.

This is a follow-up to #1637, which added inmemory to the extension's documentSelector. That change works on Mac/Linux but not on Windows because the LSP server's did_open rejects inmemory URIs on that platform.

Root cause

When did_open receives an inmemory URI like inmemory:/repl-python-<uuid>, it calls Url::to_file_path(). That method doesn't check the URI scheme, it just converts path segments into a platform path. On Mac/Linux this happens to succeed (producing /repl-python-<uuid>), but on Windows it fails because file_url_segments_to_pathbuf_windows requires the first path segment to be a drive letter like C:.

After to_file_path() fails, the fallback in did_open only accepts untitled, so inmemory documents are silently rejected on Windows and never registered. But the fallback should work for both schemes.

Fix

Extend the scheme check in did_open to also accept inmemory, routing it through the UnsavedFileTracker. This makes the behavior consistent across platforms instead of relying on to_file_path() accidentally succeeding on Unix.

I added tests for semantic tokens and completions on inmemory documents, mirroring the existing untitled tests, so regressions here will be caught going forward.

Test Plan

• Existing unsaved_file tests still pass
• New tests pass
• Verified completions and semantic highlighting work in Positron Console on Windows
• Verified they still work in Positron Console on Mac
• Ran test.py (no changes)

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

[rchen152]

Thank you!

[meta-codesync]

@rchen152 has imported this pull request. If you are a Meta employee, you can view this in D100894098.

[kinto0]

Review automatically exported from Phabricator review in Meta.

[meta-codesync]

@rchen152 merged this pull request in b812c8a.