feat: add QML language support via Qt's qmlls

[weiconghe]

Issue for this PR

Closes #1381

Type of change

• New feature (non-breaking change which adds functionality)

What does this PR do?

Adds QML (Qt Modeling Language) language support to Serena using Qt's official qmlls (or qmlls6) language server.

Implementation details:

• New QmlLanguageServer class in src/solidlsp/language_servers/qml_language_server.py that discovers the qmlls6 or qmlls binary from PATH (same pattern as Crystal/Crystalline)
• Registered QML language in ls_config.py with .qml file extension
• The server looks for qmlls6 first (Qt 6), then falls back to qmlls

User setup:
Users need to have Qt 6 installed with qmlls (or qmlls6) available on PATH. Qt ships this binary with the Qt 6 SDK. The language server is a standard LSP implementation, so all standard Serena features (document symbols, go-to-definition, references, etc.) should work.

How did you verify your code works?

• Verified language registration: Language.QML resolves correctly, file extension matching works, and get_ls_class() returns QmlLanguageServer
• Added test repository with QML source files (src/main.qml, src/shapes.qml)
• Added basic test suite that validates server startup and document symbol retrieval
• Tests are automatically skipped when qmlls/qmlls6 is not on PATH (guarded by language_tests_enabled)
• All 24 existing test_file_system.py tests continue to pass

Checklist

• I have tested my changes locally
• I have included no unrelated changes

Screenshots / recordings

N/A

[opcode81]

Thanks for your PR!

Please address the changed interface (see comment) and add an entry to the changelog.

[weiconghe]

Thanks for the review! Addressed both points:

1. Rebased onto main and adapted to the new interface:

   • Switched from ProcessLaunchInfo to the LanguageServerDependencyProviderSinglePath pattern — _find_qmlls is now _get_or_install_core_dependency inside an inner DependencyProvider class. As a side benefit, the standard ls_path / ls_args / ls_extra_args overrides now work for qmlls.
   • Renamed _get_initialize_params(repository_absolute_path) → _create_base_initialize_params() (no args), returning only the capabilities; processId / rootPath / rootUri / workspaceFolders are left to the default InitializeParamsBuilder.

2. Added a CHANGELOG entry under Language Servers.

Also dropped an unrelated already-merged commit (file_system scandir fix, PR #1634) that had accidentally landed on this branch, so the PR is now a single clean commit.

[weiconghe]

Update: I verified the server against a real qmlls locally (qmlls 0.6 standalone) and it exposed two wrong assertions in my own test suite — qmlls names QML objects by their type (ApplicationWindow, Button, Rectangle, Text), not by their id. The original assertions (mainWindow, customRect, ...) were checking id values that qmlls never surfaces as symbol names. Fixed in 7955076c; all 3 tests now pass against the real binary (server start + document symbols for both files).

Heads-up: qmlls is not installed in CI (no Qt setup in .github/workflows), so these tests currently skip in CI rather than running — they only run where qmlls/qmlls6 is on PATH. Per the add-language guide ("tests should run in CI"), it'd be worth wiring up a CI install step (qmlls ships standalone, so a small download would suffice). Happy to add that here or in a follow-up — let me know your preference.

[opcode81]

qmlls is not installed in CI

I am aware of this. However, CI was recently restructured by @MischaPanch and I would leave it up to him to decide whether QML should be tested and, if so, in which part of the matrix.