Honor parameter information setting for signature help

[Stella Huang (StellaHuang95)]

Context

PTVS historically honored Visual Studio's LANGPREFERENCES.fAutoListParams value before starting parameter information. After signature help moved to the Visual Studio LSP client and Pylance, automatic sessions were instead driven directly by Pylance's advertised trigger characters. As a result, disabling Parameter information no longer affected Python signature help.

The stock Statement completion group was later hidden because its other settings are not supported by the current LSP-based experience, so this change exposes only the setting that is now supported.

Fixes #8580

Changes

• Add Parameter information to Text Editor > Python > Advanced.
• Persist the option through the existing Python LANGPREFERENCES2.fAutoListParams value, preserving existing user preferences and Visual Studio settings behavior.
• Add a Python language-client middle layer for textDocument/signatureHelp requests.
• Suppress only unambiguous initial automatic requests (TriggerCharacter or ContentChange) when the option is disabled.
• Continue forwarding explicit Edit > IntelliSense > Parameter Info invocations, active-session updates, and retriggers.
• Fail open for missing, malformed, or future request context shapes so ambiguous requests retain the existing behavior.
• Publish live preference changes safely to LSP request threads through the existing LanguagePreferences service.
• Use the current generic middle-layer API on VS 18 and the compatible legacy API on VS 17.

Behavior and compatibility

When the option is enabled, signature help behaves exactly as before. Disabling it prevents new automatic popups without disabling the explicit Parameter Info command or interrupting an already active session.

The middle layer handles only textDocument/signatureHelp; completion, hover, diagnostics, navigation, formatting, and other LSP features are unaffected. Pylance capabilities and configuration are unchanged.

ShowCompletion remains disabled, so this does not reintroduce the unsupported stock Auto list members and Hide advanced members controls.

Validation

• Full Debug18 Python traversal build: succeeded with 0 warnings and 0 errors.
• Focused Debug18 PythonTools.csproj rebuild: succeeded with 0 warnings and 0 errors.
• VS 17 compatibility compile: completed with 0 errors when pre-existing warnings were not promoted to errors.
• Final editor diagnostics and git diff --check: clean.

Automated tests are not included in this change.

[azure-pipelines]

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[Heejae Chang (heejaechang)]

🔒 Automated review in progress — Heejae Chang (@heejaechang) is auto-reviewing this PR.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Stella Huang (StellaHuang95)]

/azp run

[azure-pipelines]

Azure Pipelines:
Successfully started running 1 pipeline(s).

[Heejae Chang (heejaechang)]

Please add focused regression coverage for the signature-help suppression matrix. This predicate has several fail-open branches, and tests should distinguish disabled preferences for new automatic TriggerCharacter/ContentChange requests from explicit invocations, retriggers, active sessions, malformed contexts, and unavailable preferences.

[Heejae Chang (heejaechang)]

Approved via Review Center.